- o ({{MathWorld | urlname=o | title=o}}): o
- O ({{MathWorld | urlname=O | title=O}}): O
- Oban Number ({{MathWorld | urlname=ObanNumber | title=Oban Number}}): Oban number
- Obelisk ({{MathWorld | urlname=Obelisk | title=Obelisk}}): Obelisk
- Obelus ({{MathWorld | urlname=Obelus | title=Obelus}}): Obelus
- Object ({{MathWorld | urlname=Object | title=Object}}): Object
- Objective Function ({{MathWorld | urlname=ObjectiveFunction | title=Objective Function}}): Objective function
- Oblate Ellipsoid ({{MathWorld | urlname=OblateEllipsoid | title=Oblate Ellipsoid}}): Oblate ellipsoid
- Oblateness ({{MathWorld | urlname=Oblateness | title=Oblateness}}): Oblateness
- Oblate Spheroid ({{MathWorld | urlname=OblateSpheroid | title=Oblate Spheroid}}): Oblate spheroid
- Oblate Spheroidal Coordinates ({{MathWorld | urlname=OblateSpheroidalCoordinates | title=Oblate Spheroidal Coordinates}}): Oblate spheroidal coordinates
- Oblate Spheroidal Wave Function ({{MathWorld | urlname=OblateSpheroidalWaveFunction | title=Oblate Spheroidal Wave Function}}): Oblate spheroidal wave function
- Oblate Spheroid Geodesic ({{MathWorld | urlname=OblateSpheroidGeodesic | title=Oblate Spheroid Geodesic}}): Oblate spheroid geodesic
- Oblique Angle ({{MathWorld | urlname=ObliqueAngle | title=Oblique angle}}): Oblique angle
- Oblique Coordinates ({{MathWorld | urlname=ObliqueCoordinates | title=Oblique coordinates}}): Oblique Coordinates
- Oblique coordinate system ({{MathWorld | urlname=ObliqueCoordinateSystem | title=Oblique Coordinate System}}): Oblique Coordinate system
- Oblique Cylinder ({{MathWorld | urlname=ObliqueCylinder | title=Oblique Cylinder}}): Oblique cylinder
- Oblique Prism ({{MathWorld | urlname=ObliquePrism | title=Oblique Prism}}): Oblique prism
- Oblique Triangle ({{MathWorld | urlname=ObliqueTriangle | title=Oblique Triangle}}): Oblique triangle
- Oblong Number ({{MathWorld | urlname=OblongNumber | title=Oblong Number}}): Oblong number
- Obstruction ({{MathWorld | urlname=Obstruction | title=Obstruction}}): Obstruction
- Obtuse Angle ({{MathWorld | urlname=ObtuseAngle | title=Obtuse Angle}}): Obtuse Angle
- Obtuse Triangle ({{MathWorld | urlname=ObtuseTriangle | title=Obtuse Triangle}}): Obtuse triangle
- Ochoa Curve ({{MathWorld | urlname=OchoaCurve | title=Ochoa Curve}}): Ochoa curve
- Ockham Algebra ({{MathWorld | urlname=OckhamAlgebra | title=Ockham Algebra}}): Ockham algebra
- Octachoron ({{MathWorld | urlname=Octachoron | title=Octachoron}}): Octachoron
- Octacontagon ({{MathWorld | urlname=Octacontagon | title=Octacontagon}}): Octacontagon
- Octadecagon ({{MathWorld | urlname=Octadecagon | title=Octadecagon}}): Octadecagon
- Octagon ({{MathWorld | urlname=Octagon | title=Octagon}}): Octagon
- Octagonal Heptagonal N... ({{MathWorld | urlname=OctagonalHeptagonalNumber | title=Octagonal Heptagonal Number}}): Octagonal heptagonal number
- Octagonal Hexagonal Nu... ({{MathWorld | urlname=OctagonalHexagonalNumber | title=Octagonal Hexagonal Number}}): Octagonal hexagonal number
- Octagonal Number ({{MathWorld | urlname=OctagonalNumber | title=Octagonal Number}}): Octagonal number
- Octagonal Pentagonal N... ({{MathWorld | urlname=OctagonalPentagonalNumber | title=Octagonal Pentagonal Number}}): Octagonal pentagonal number
- Octagonal Prism ({{MathWorld | urlname=OctagonalPrism | title=Octagonal Prism}}): Octagonal prism
- Octagonal Square Number ({{MathWorld | urlname=OctagonalSquareNumber | title=Octagonal Square Number}}): Octagonal square number
- Octagonal Triangular N... ({{MathWorld | urlname=OctagonalTriangularNumber | title=Octagonal Triangular Number}}): Octagonal triangular number
- Octagram ({{MathWorld | urlname=Octagram | title=Octagram}}): Octagram
- Octahedral Equation ({{MathWorld | urlname=OctahedralEquation | title=Octahedral Equation}}): Octahedral equation
- Octahedral Graph ({{MathWorld | urlname=OctahedralGraph | title=Octahedral Graph}}): Octahedral graph
- Octahedral Group ({{MathWorld | urlname=OctahedralGroup | title=Octahedral Group}}): Octahedral group
- Octahedral Number ({{MathWorld | urlname=OctahedralNumber | title=Octahedral Number}}): Octahedral number
- Octahedron ({{MathWorld | urlname=Octahedron | title=Octahedron}}): Octahedron
- Octahedron 10-Compound ({{MathWorld | urlname=Octahedron10-Compound | title=Octahedron 10-Compound}}): Octahedron 10-compound
- Octahedron 2-Compound ({{MathWorld | urlname=Octahedron2-Compound | title=Octahedron 2-Compound}}): Octahedron 2-compound
- Octahedron 3-Compound ({{MathWorld | urlname=Octahedron3-Compound | title=Octahedron 3-Compound}}): Octahedron 3-compound
- Octahedron 4-Compound ({{MathWorld | urlname=Octahedron4-Compound | title=Octahedron 4-Compound}}): Octahedron 4-compound
- Octahedron 5-Compound ({{MathWorld | urlname=Octahedron5-Compound | title=Octahedron 5-Compound}}): Octahedron 5-compound
- Octahedron 6-Compound ({{MathWorld | urlname=Octahedron6-Compound | title=Octahedron 6-Compound}}): Octahedron 6-compound
- Octahedron Stellation ({{MathWorld | urlname=OctahedronStellation | title=Octahedron Stellation}}): Octahedron stellation
- Octahedron Tetrahedron Picking ({{MathWorld | urlname=OctahedronTetrahedronPicking | title=Octahedron Tetrahedron...}}): Octahedron tetrahedron picking
- Octahemioctacron ({{MathWorld | urlname=Octahemioctacron | title=Octahemioctacron}}): Octahemioctacron
- Octahemioctahedron ({{MathWorld | urlname=Octahemioctahedron | title=Octahemioctahedron}}): Octahemioctahedron
- Octakaidecagon ({{MathWorld | urlname=Octakaidecagon | title=Octakaidecagon}}): Octakaidecagon
- Octal ({{MathWorld | urlname=Octal | title=Octal}}): Octal
- Octant ({{MathWorld | urlname=Octant | title=Octant}}): Octant
- Octatetracontagon ({{MathWorld | urlname=Octatetracontagon | title=Octatetracontagon}}): Octatetracontagon
- Octatetrahedron ({{MathWorld | urlname=Octatetrahedron | title=Octatetrahedron}}): Octatetrahedron
- Octave ({{MathWorld | urlname=Octave | title=Octave}}): Octave
- Octdong Surface ({{MathWorld | urlname=OctdongSurface | title=Octdong Surface}}): Octdong surface
- Octiamond ({{MathWorld | urlname=Octiamond | title=Octiamond}}): Octiamond
- Octiamond Tiling ({{MathWorld | urlname=OctiamondTiling | title=Octiamond Tiling}}): Octiamond tiling
- Octic Curve ({{MathWorld | urlname=OcticCurve | title=Octic Curve}}): Octic curve
- Octic Graph ({{MathWorld | urlname=OcticGraph | title=Octic Graph}}): Octic graph
- Octic Reciprocity Theorem ({{MathWorld | urlname=OcticReciprocityTheorem | title=Octic Reciprocity Theorem}}): Octic reciprocity theorem
- Octic Surface ({{MathWorld | urlname=OcticSurface | title=Octic Surface}}): Octic surface
- Octillion ({{MathWorld | urlname=Octillion | title=Octillion}}): Octillion
- Octodecillion ({{MathWorld | urlname=Octodecillion | title=Octodecillion}}): Octodecillion
- Octomino ({{MathWorld | urlname=Octomino | title=Octomino}}): Octomino
- Octonion ({{MathWorld | urlname=Octonion | title=Octonion}}): Octonion
- Octothorpe ({{MathWorld | urlname=Octothorpe | title=Octothorpe}}): Octothorpe
- Odd Divisor Function ({{MathWorld | urlname=OddDivisorFunction | title=Odd Divisor Function}}): Odd divisor function
- Oddest Prime ({{MathWorld | urlname=OddestPrime | title=Oddest Prime}}): Oddest prime
- Odd Function ({{MathWorld | urlname=OddFunction | title=Odd Function}}): Odd function
- Odd Graph ({{MathWorld | urlname=OddGraph | title=Odd Graph}}): Odd graph
- Odd Node ({{MathWorld | urlname=OddNode | title=Odd Node}}): Odd node
- Odd Number ({{MathWorld | urlname=OddNumber | title=Odd Number}}): Odd number
- Odd Number Theorem ({{MathWorld | urlname=OddNumberTheorem | title=Odd Number Theorem}}): Odd number theorem
- Odd Order Theorem ({{MathWorld | urlname=OddOrderTheorem | title=Odd Order Theorem}}): Odd order theorem
- Odd Part ({{MathWorld | urlname=OddPart | title=Odd Part}}): Odd part
- Odd Perfect Number ({{MathWorld | urlname=OddPerfectNumber | title=Odd Perfect Number}}): Odd perfect number
- Odd Permutation ({{MathWorld | urlname=OddPermutation | title=Odd Permutation}}): Odd permutation
- Odd Power ({{MathWorld | urlname=OddPower | title=Odd Power}}): Odd power
- Odd Prime ({{MathWorld | urlname=OddPrime | title=Odd Prime}}): Odd prime
- Odds ({{MathWorld | urlname=Odds | title=Odds}}): Odds
- Odd Sequence ({{MathWorld | urlname=OddSequence | title=Odd Sequence}}): Odd sequence
- Odd Triple ({{MathWorld | urlname=OddTriple | title=Odd Triple}}): Odd triple
- Odd Vertex ({{MathWorld | urlname=OddVertex | title=Odd Vertex}}): Odd vertex
- ODE ({{MathWorld | urlname=ODE | title=ODE}}): ODE
- Odious Number ({{MathWorld | urlname=OdiousNumber | title=Odious Number}}): Odious number
- Oesterlé-Masser Conjec... ({{MathWorld | urlname=Oesterle-MasserConjecture | title=Oesterlé-Masser Conjec...}}): Oesterlé-Masser Conjec...
- Offset Curves ({{MathWorld | urlname=OffsetCurves | title=Offset Curves}}): Offset Curves
- Offset Rings ({{MathWorld | urlname=OffsetRings | title=Offset Rings}}): Offset Rings
- Of Order ({{MathWorld | urlname=OfOrder | title=Of Order}}): Of Order
- Of Shape ({{MathWorld | urlname=OfShape | title=Of Shape}}): Of Shape
- Of the Form ({{MathWorld | urlname=OftheForm | title=Of the Form}}): Of the Form
- Ogive ({{MathWorld | urlname=Ogive | title=Ogive}}): Ogive
- Oldknow Points ({{MathWorld | urlname=OldknowPoints | title=Oldknow Points}}): Oldknow Points
- Oliveira's Minimal Sur... ({{MathWorld | urlname=OliveirasMinimalSurface | title=Oliveira's Minimal Sur...}}): Oliveira's Minimal Sur...
- Oloid ({{MathWorld | urlname=Oloid | title=Oloid}}): Oloid
- omega2 Constant ({{MathWorld | urlname=Omega-2Constant | title=omega2 Constant}}): omega2 Constant
- Omega Constant ({{MathWorld | urlname=OmegaConstant | title=Omega Constant}}): Omega Constant
- Omega Function ({{MathWorld | urlname=OmegaFunction | title=Omega Function}}): Omega Function
- Omino ({{MathWorld | urlname=Omino | title=Omino}}): Omino
- Omnific Integer ({{MathWorld | urlname=OmnificInteger | title=Omnific Integer}}): Omnific Integer
- O'Nan Group ({{MathWorld | urlname=ONanGroup | title=O'Nan Group}}): O'Nan Group
- Onduloid ({{MathWorld | urlname=Onduloid | title=Onduloid}}): Onduloid
- One ({{MathWorld | urlname=One | title=One}}): One
- One and Only One ({{MathWorld | urlname=OneandOnlyOne | title=One and Only One}}): One and Only One
- One-Form ({{MathWorld | urlname=One-Form | title=One-Form}}): One-Form
- One-Max Property ({{MathWorld | urlname=One-MaxProperty | title=One-Max Property}}): One-Max Property
- One-Mouth Theorem ({{MathWorld | urlname=One-MouthTheorem | title=One-Mouth Theorem}}): One-Mouth Theorem
- One-Ninth Constant ({{MathWorld | urlname=One-NinthConstant | title=One-Ninth Constant}}): One-Ninth Constant
- One-One Complete ({{MathWorld | urlname=One-OneComplete | title=One-One Complete}}): One-One Complete
- One-Point Compactifica... ({{MathWorld | urlname=One-PointCompactification | title=One-Point Compactifica...}}): One-Point Compactifica...
- One-Seventh Ellipse ({{MathWorld | urlname=One-SeventhEllipse | title=One-Seventh Ellipse}}): One-Seventh Ellipse
- One-Sheeted Hyperboloid ({{MathWorld | urlname=One-SheetedHyperboloid | title=One-Sheeted Hyperboloid}}): One-Sheeted Hyperboloid
- One-Sided Ideal ({{MathWorld | urlname=One-SidedIdeal | title=One-Sided Ideal}}): One-Sided Ideal
- One-Term Relation ({{MathWorld | urlname=One-TermRelation | title=One-Term Relation}}): One-Term Relation
- One-to-One ({{MathWorld | urlname=One-to-One | title=One-to-One}}): One-to-One
- One-to-One Correspondence ({{MathWorld | urlname=One-to-OneCorrespondence | title=One-to-One Correspondence}}): One-to-One Correspondence
- One-Way Function ({{MathWorld | urlname=One-WayFunction | title=One-Way Function}}): One-Way Function
- One-Way Hash Function ({{MathWorld | urlname=One-WayHashFunction | title=One-Way Hash Function}}): One-Way Hash Function
- Only Critical Point in... ({{MathWorld | urlname=OnlyCriticalPointinTownTest | title=Only Critical Point in...}}): Only Critical Point in...
- Ono Inequality ({{MathWorld | urlname=OnoInequality | title=Ono Inequality}}): Ono Inequality
- O-Notation ({{MathWorld | urlname=O-Notation | title=O-Notation}}): O-Notation
- Onsager Differential E... ({{MathWorld | urlname=OnsagerDifferentialEquation | title=Onsager Differential E...}}): Onsager Differential E...
- Onto ({{MathWorld | urlname=Onto | title=Onto}}): Onto
- Open ({{MathWorld | urlname=Open | title=Open}}): Open
- Open Ball ({{MathWorld | urlname=OpenBall | title=Open Ball}}): Open Ball
- Open Cover ({{MathWorld | urlname=OpenCover | title=Open Cover}}): Open Cover
- Open Disk ({{MathWorld | urlname=OpenDisk | title=Open Disk}}): Open Disk
- Opening Angle ({{MathWorld | urlname=OpeningAngle | title=Opening Angle}}): Opening Angle
- Open Interval ({{MathWorld | urlname=OpenInterval | title=Open Interval}}): Open Interval
- Open Manifold ({{MathWorld | urlname=OpenManifold | title=Open Manifold}}): Open Manifold
- Open Map ({{MathWorld | urlname=OpenMap | title=Open Map}}): Open Map
- Open Mapping Theorem ({{MathWorld | urlname=OpenMappingTheorem | title=Open Mapping Theorem}}): Open Mapping Theorem
- Open Neighborhood ({{MathWorld | urlname=OpenNeighborhood | title=Open Neighborhood}}): Open Neighborhood
- Open Problems ({{MathWorld | urlname=OpenProblems | title=Open Problems}}): Open Problems
- Open Sentential Formula ({{MathWorld | urlname=OpenSententialFormula | title=Open Sentential Formula}}): Open Sentential Formula
- Open Set ({{MathWorld | urlname=OpenSet | title=Open Set}}): Open Set
- Operad ({{MathWorld | urlname=Operad | title=Operad}}): Operad
- Operand ({{MathWorld | urlname=Operand | title=Operand}}): Operand
- Operation ({{MathWorld | urlname=Operation | title=Operation}}): Operation
- Operational Mathematics ({{MathWorld | urlname=OperationalMathematics | title=Operational Mathematics}}): Operational Mathematics
- Operations Research ({{MathWorld | urlname=OperationsResearch | title=Operations Research}}): Operations Research
- Operator ({{MathWorld | urlname=Operator | title=Operator}}): Operator
- Operator Calculus ({{MathWorld | urlname=OperatorCalculus | title=Operator Calculus}}): Operator Calculus
- Operator Norm ({{MathWorld | urlname=OperatorNorm | title=Operator Norm}}): Operator Norm
- Operator Spectrum ({{MathWorld | urlname=OperatorSpectrum | title=Operator Spectrum}}): Operator Spectrum
- Operator Theory ({{MathWorld | urlname=OperatorTheory | title=Operator Theory}}): Operator Theory
- Ophiuride ({{MathWorld | urlname=Ophiuride | title=Ophiuride}}): Ophiuride
- Opposite Side ({{MathWorld | urlname=OppositeSide | title=Opposite Side}}): Opposite Side
- Optical Illusion ({{MathWorld | urlname=OpticalIllusion | title=Optical Illusion}}): Optical Illusion
- Optimal Golomb Ruler ({{MathWorld | urlname=OptimalGolombRuler | title=Optimal Golomb Ruler}}): Optimal Golomb Ruler
- Optimization ({{MathWorld | urlname=Optimization | title=Optimization}}): Optimization
- Optimization Theory ({{MathWorld | urlname=OptimizationTheory | title=Optimization Theory}}): Optimization Theory
- Optimum ({{MathWorld | urlname=Optimum | title=Optimum}}): Optimum
- Or ({{MathWorld | urlname=Or | title=Or}}): Or
- OR ({{MathWorld | urlname=OR | title=OR}}): OR
- Oracle ({{MathWorld | urlname=Oracle | title=Oracle}}): Oracle
- Orbifold ({{MathWorld | urlname=Orbifold | title=Orbifold}}): Orbifold
- Orbifold Notation ({{MathWorld | urlname=OrbifoldNotation | title=Orbifold Notation}}): Orbifold Notation
- Orbison's Illusion ({{MathWorld | urlname=OrbisonsIllusion | title=Orbison's Illusion}}): Orbison's Illusion
- Orbit-Counting Theorem ({{MathWorld | urlname=Orbit-CountingTheorem | title=Orbit-Counting Theorem}}): Orbit-Counting Theorem
- Orchard-Planting Problem ({{MathWorld | urlname=Orchard-PlantingProblem | title=Orchard-Planting Problem}}): Orchard-Planting Problem
- Orchard Problem ({{MathWorld | urlname=OrchardProblem | title=Orchard Problem}}): Orchard Problem
- Orchard Visibility Pro... ({{MathWorld | urlname=OrchardVisibilityProblem | title=Orchard Visibility Pro...}}): Orchard Visibility Pro...
- Order ({{MathWorld | urlname=Order | title=Order}}): Order
- Ordered Factorization ({{MathWorld | urlname=OrderedFactorization | title=Ordered Factorization}}): Ordered Factorization
- Ordered Geometry ({{MathWorld | urlname=OrderedGeometry | title=Ordered Geometry}}): Ordered Geometry
- Ordered List ({{MathWorld | urlname=OrderedList | title=Ordered List}}): Ordered List
- Ordered Pair ({{MathWorld | urlname=OrderedPair | title=Ordered Pair}}): Ordered Pair
- Ordered Pairs Represen... ({{MathWorld | urlname=OrderedPairsRepresentation | title=Ordered Pairs Represen...}}): Ordered Pairs Represen...
- Ordered Set ({{MathWorld | urlname=OrderedSet | title=Ordered Set}}): Ordered Set
- Ordered Tree ({{MathWorld | urlname=OrderedTree | title=Ordered Tree}}): Ordered Tree
- Ordering ({{MathWorld | urlname=Ordering | title=Ordering}}): Ordering
- Ordering Axioms ({{MathWorld | urlname=OrderingAxioms | title=Ordering Axioms}}): Ordering Axioms
- Order Isomorphic ({{MathWorld | urlname=OrderIsomorphic | title=Order Isomorphic}}): Order Isomorphic
- Orderless ({{MathWorld | urlname=Orderless | title=Orderless}}): Orderless
- Order of Magnitude ({{MathWorld | urlname=OrderofMagnitude | title=Order of Magnitude}}): Order of Magnitude
- Order Statistic ({{MathWorld | urlname=OrderStatistic | title=Order Statistic}}): Order Statistic
- Order Topology ({{MathWorld | urlname=OrderTopology | title=Order Topology}}): Order Topology
- Order Type ({{MathWorld | urlname=OrderType | title=Order Type}}): Order Type
- Ordinal ({{MathWorld | urlname=Ordinal | title=Ordinal}}): Ordinal
- Ordinal Addition ({{MathWorld | urlname=OrdinalAddition | title=Ordinal Addition}}): Ordinal Addition
- Ordinal Comparison ({{MathWorld | urlname=OrdinalComparison | title=Ordinal Comparison}}): Ordinal Comparison
- Ordinal Exponentiation ({{MathWorld | urlname=OrdinalExponentiation | title=Ordinal Exponentiation}}): Ordinal Exponentiation
- Ordinal Multiplication ({{MathWorld | urlname=OrdinalMultiplication | title=Ordinal Multiplication}}): Ordinal Multiplication
- Ordinal Number ({{MathWorld | urlname=OrdinalNumber | title=Ordinal Number}}): Ordinal Number
- Ordinary Differential... ({{MathWorld | urlname=OrdinaryDifferentialEquation | title=Ordinary Differential...}}): Ordinary Differential...
- Ordinary Differential... ({{MathWorld | urlname=OrdinaryDifferentialEquationOrder | title=Ordinary Differential...}}): Ordinary Differential...
- Ordinary Differential... ({{MathWorld | urlname=OrdinaryDifferentialEquationSystemwithConstantCoefficients | title=Ordinary Differential...}}): Ordinary Differential...
- Ordinary Double Point ({{MathWorld | urlname=OrdinaryDoublePoint | title=Ordinary Double Point}}): Ordinary Double Point
- Ordinary Generating Fu... ({{MathWorld | urlname=OrdinaryGeneratingFunction | title=Ordinary Generating Fu...}}): Ordinary Generating Fu...
- Ordinary Line ({{MathWorld | urlname=OrdinaryLine | title=Ordinary Line}}): Ordinary Line
- Ordinary Point ({{MathWorld | urlname=OrdinaryPoint | title=Ordinary Point}}): Ordinary Point
- Ordinary Surface ({{MathWorld | urlname=OrdinarySurface | title=Ordinary Surface}}): Ordinary Surface
- Ordinary Topology ({{MathWorld | urlname=OrdinaryTopology | title=Ordinary Topology}}): Ordinary Topology
- Ordinate ({{MathWorld | urlname=Ordinate | title=Ordinate}}): Ordinate
- Ore Algebra ({{MathWorld | urlname=OreAlgebra | title=Ore Algebra}}): Ore Algebra
- Ore Graph ({{MathWorld | urlname=OreGraph | title=Ore Graph}}): Ore Graph
- Ore Number ({{MathWorld | urlname=OreNumber | title=Ore Number}}): Ore Number
- Ore's Conjecture ({{MathWorld | urlname=OresConjecture | title=Ore's Conjecture}}): Ore's Conjecture
- Ore's Theorem ({{MathWorld | urlname=OresTheorem | title=Ore's Theorem}}): Ore's Theorem
- Orientable Manifold ({{MathWorld | urlname=OrientableManifold | title=Orientable Manifold}}): Orientable Manifold
- Orientable Surface ({{MathWorld | urlname=OrientableSurface | title=Orientable Surface}}): Orientable Surface
- Orientation ({{MathWorld | urlname=Orientation | title=Orientation}}): Orientation
- Orientation-Preserving ({{MathWorld | urlname=Orientation-Preserving | title=Orientation-Preserving}}): Orientation-Preserving
- Orientation-Reversing ({{MathWorld | urlname=Orientation-Reversing | title=Orientation-Reversing}}): Orientation-Reversing
- Oriented Graph ({{MathWorld | urlname=OrientedGraph | title=Oriented Graph}}): Oriented Graph
- Oriented Knot ({{MathWorld | urlname=OrientedKnot | title=Oriented Knot}}): Oriented Knot
- Oriented Link ({{MathWorld | urlname=OrientedLink | title=Oriented Link}}): Oriented Link
- Oriented Matroid ({{MathWorld | urlname=OrientedMatroid | title=Oriented Matroid}}): Oriented Matroid
- Oriented Surface ({{MathWorld | urlname=OrientedSurface | title=Oriented Surface}}): Oriented Surface
- Oriented Tree ({{MathWorld | urlname=OrientedTree | title=Oriented Tree}}): Oriented Tree
- Origami ({{MathWorld | urlname=Origami | title=Origami}}): Origami
- Origin ({{MathWorld | urlname=Origin | title=Origin}}): Origin
- Original Triangle ({{MathWorld | urlname=OriginalTriangle | title=Original Triangle}}): Original Triangle
- Ornstein's Theorem ({{MathWorld | urlname=OrnsteinsTheorem | title=Ornstein's Theorem}}): Ornstein's Theorem
- Orr-Sommerfeld Differe... ({{MathWorld | urlname=Orr-SommerfeldDifferentialEquation | title=Orr-Sommerfeld Differe...}}): Orr-Sommerfeld Differe...
- Orr's Theorem ({{MathWorld | urlname=OrrsTheorem | title=Orr's Theorem}}): Orr's Theorem
- Orthic Axis ({{MathWorld | urlname=OrthicAxis | title=Orthic Axis}}): Orthic Axis
- Orthic Circle ({{MathWorld | urlname=OrthicCircle | title=Orthic Circle}}): Orthic Circle
- Orthic Inconic ({{MathWorld | urlname=OrthicInconic | title=Orthic Inconic}}): Orthic Inconic
- Orthic Triangle ({{MathWorld | urlname=OrthicTriangle | title=Orthic Triangle}}): Orthic Triangle
- Orthobicupola ({{MathWorld | urlname=Orthobicupola | title=Orthobicupola}}): Orthobicupola
- Orthobirotunda ({{MathWorld | urlname=Orthobirotunda | title=Orthobirotunda}}): Orthobirotunda
- Orthocenter ({{MathWorld | urlname=Orthocenter | title=Orthocenter}}): Orthocenter
- Orthocentric Centroid ({{MathWorld | urlname=OrthocentricCentroid | title=Orthocentric Centroid}}): Orthocentric Centroid
- Orthocentric Coordinates ({{MathWorld | urlname=OrthocentricCoordinates | title=Orthocentric Coordinates}}): Orthocentric Coordinates
- Orthocentric Line ({{MathWorld | urlname=OrthocentricLine | title=Orthocentric Line}}): Orthocentric Line
- Orthocentric Quadrangle ({{MathWorld | urlname=OrthocentricQuadrangle | title=Orthocentric Quadrangle}}): Orthocentric Quadrangle
- Orthocentric Quadrilat... ({{MathWorld | urlname=OrthocentricQuadrilateral | title=Orthocentric Quadrilat...}}): Orthocentric Quadrilat...
- Orthocentric System ({{MathWorld | urlname=OrthocentricSystem | title=Orthocentric System}}): Orthocentric System
- Orthocentroidal Circle ({{MathWorld | urlname=OrthocentroidalCircle | title=Orthocentroidal Circle}}): Orthocentroidal Circle
- Orthocorrespondent ({{MathWorld | urlname=Orthocorrespondent | title=Orthocorrespondent}}): Orthocorrespondent
- Orthocubic ({{MathWorld | urlname=Orthocubic | title=Orthocubic}}): Orthocubic
- Orthocupolarotunda ({{MathWorld | urlname=Orthocupolarotunda | title=Orthocupolarotunda}}): Orthocupolarotunda
- Orthodiagonal Quadrangle ({{MathWorld | urlname=OrthodiagonalQuadrangle | title=Orthodiagonal Quadrangle}}): Orthodiagonal Quadrangle
- Orthodrome ({{MathWorld | urlname=Orthodrome | title=Orthodrome}}): Orthodrome
- Orthogonal ({{MathWorld | urlname=Orthogonal | title=Orthogonal}}): Orthogonal
- Orthogonal Array ({{MathWorld | urlname=OrthogonalArray | title=Orthogonal Array}}): Orthogonal Array
- Orthogonal Basis ({{MathWorld | urlname=OrthogonalBasis | title=Orthogonal Basis}}): Orthogonal Basis
- Orthogonal Circles ({{MathWorld | urlname=OrthogonalCircles | title=Orthogonal Circles}}): Orthogonal Circles
- Orthogonal Complement ({{MathWorld | urlname=OrthogonalComplement | title=Orthogonal Complement}}): Orthogonal Complement
- Orthogonal Coordinate... ({{MathWorld | urlname=OrthogonalCoordinateSystem | title=Orthogonal Coordinate...}}): Orthogonal Coordinate...
- Orthogonal Curves ({{MathWorld | urlname=OrthogonalCurves | title=Orthogonal Curves}}): Orthogonal Curves
- Orthogonal Decomposition ({{MathWorld | urlname=OrthogonalDecomposition | title=Orthogonal Decomposition}}): Orthogonal Decomposition
- Orthogonal Functions ({{MathWorld | urlname=OrthogonalFunctions | title=Orthogonal Functions}}): Orthogonal Functions
- Orthogonal Group ({{MathWorld | urlname=OrthogonalGroup | title=Orthogonal Group}}): Orthogonal Group
- Orthogonal Group Repre... ({{MathWorld | urlname=OrthogonalGroupRepresentations | title=Orthogonal Group Repre...}}): Orthogonal Group Repre...
- Orthogonal Involution ({{MathWorld | urlname=OrthogonalInvolution | title=Orthogonal Involution}}): Orthogonal Involution
- Orthogonality Condition ({{MathWorld | urlname=OrthogonalityCondition | title=Orthogonality Condition}}): Orthogonality Condition
- Orthogonality Theorem ({{MathWorld | urlname=OrthogonalityTheorem | title=Orthogonality Theorem}}): Orthogonality Theorem
- Orthogonal Lie Algebra ({{MathWorld | urlname=OrthogonalLieAlgebra | title=Orthogonal Lie Algebra}}): Orthogonal Lie Algebra
- Orthogonal Lines ({{MathWorld | urlname=OrthogonalLines | title=Orthogonal Lines}}): Orthogonal Lines
- Orthogonal Matrix ({{MathWorld | urlname=OrthogonalMatrix | title=Orthogonal Matrix}}): Orthogonal Matrix
- Orthogonal Polynomials ({{MathWorld | urlname=OrthogonalPolynomials | title=Orthogonal Polynomials}}): Orthogonal Polynomials
- Orthogonal Projection ({{MathWorld | urlname=OrthogonalProjection | title=Orthogonal Projection}}): Orthogonal Projection
- Orthogonal Rotation Group ({{MathWorld | urlname=OrthogonalRotationGroup | title=Orthogonal Rotation Group}}): Orthogonal Rotation Group
- Orthogonal Set ({{MathWorld | urlname=OrthogonalSet | title=Orthogonal Set}}): Orthogonal Set
- Orthogonal Subspaces ({{MathWorld | urlname=OrthogonalSubspaces | title=Orthogonal Subspaces}}): Orthogonal Subspaces
- Orthogonal Sum ({{MathWorld | urlname=OrthogonalSum | title=Orthogonal Sum}}): Orthogonal Sum
- Orthogonal Surfaces ({{MathWorld | urlname=OrthogonalSurfaces | title=Orthogonal Surfaces}}): Orthogonal Surfaces
- Orthogonal Tensors ({{MathWorld | urlname=OrthogonalTensors | title=Orthogonal Tensors}}): Orthogonal Tensors
- Orthogonal Transformation ({{MathWorld | urlname=OrthogonalTransformation | title=Orthogonal Transformation}}): Orthogonal Transformation
- Orthogonal Vectors ({{MathWorld | urlname=OrthogonalVectors | title=Orthogonal Vectors}}): Orthogonal Vectors
- Orthographic Projection ({{MathWorld | urlname=OrthographicProjection | title=Orthographic Projection}}): Orthographic Projection
- Orthoharmonic ({{MathWorld | urlname=Orthoharmonic | title=Orthoharmonic}}): Orthoharmonic
- Orthojoin ({{MathWorld | urlname=Orthojoin | title=Orthojoin}}): Orthojoin
- Orthologic Triangles ({{MathWorld | urlname=OrthologicTriangles | title=Orthologic Triangles}}): Orthologic Triangles
- Orthology Center ({{MathWorld | urlname=OrthologyCenter | title=Orthology Center}}): Orthology Center
- Orthomorphic Projection ({{MathWorld | urlname=OrthomorphicProjection | title=Orthomorphic Projection}}): Orthomorphic Projection
- Orthomorphism ({{MathWorld | urlname=Orthomorphism | title=Orthomorphism}}): Orthomorphism
- Orthonormal Basis ({{MathWorld | urlname=OrthonormalBasis | title=Orthonormal Basis}}): Orthonormal Basis
- Orthonormal Functions ({{MathWorld | urlname=OrthonormalFunctions | title=Orthonormal Functions}}): Orthonormal Functions
- Orthonormal Set ({{MathWorld | urlname=OrthonormalSet | title=Orthonormal Set}}): Orthonormal Set
- Orthonormal Transforma... ({{MathWorld | urlname=OrthonormalTransformation | title=Orthonormal Transforma...}}): Orthonormal Transforma...
- Orthonormal Vectors ({{MathWorld | urlname=OrthonormalVectors | title=Orthonormal Vectors}}): Orthonormal Vectors
- Orthoplex ({{MathWorld | urlname=Orthoplex | title=Orthoplex}}): Orthoplex
- Orthopolar Line ({{MathWorld | urlname=OrthopolarLine | title=Orthopolar Line}}): Orthopolar Line
- Orthopole ({{MathWorld | urlname=Orthopole | title=Orthopole}}): Orthopole
- Orthoptic Circle of th... ({{MathWorld | urlname=OrthopticCircleoftheSteinerInellipse | title=Orthoptic Circle of th...}}): Orthoptic Circle of th...
- Orthoptic Curve ({{MathWorld | urlname=OrthopticCurve | title=Orthoptic Curve}}): Orthoptic Curve
- Orthosymmetric Matrix ({{MathWorld | urlname=OrthosymmetricMatrix | title=Orthosymmetric Matrix}}): Orthosymmetric Matrix
- Orthotomic ({{MathWorld | urlname=Orthotomic | title=Orthotomic}}): Orthotomic
- Orthotope ({{MathWorld | urlname=Orthotope | title=Orthotope}}): Orthotope
- Orthotransversal ({{MathWorld | urlname=Orthotransversal | title=Orthotransversal}}): Orthotransversal
- Osborn's Rule ({{MathWorld | urlname=OsbornsRule | title=Osborn's Rule}}): Osborn's Rule
- Oscillating Function ({{MathWorld | urlname=OscillatingFunction | title=Oscillating Function}}): Oscillating Function
- Oscillation ({{MathWorld | urlname=Oscillation | title=Oscillation}}): Oscillation
- Oscillation Land ({{MathWorld | urlname=OscillationLand | title=Oscillation Land}}): Oscillation Land
- Oscillatory Function ({{MathWorld | urlname=OscillatoryFunction | title=Oscillatory Function}}): Oscillatory Function
- Osculating Circle ({{MathWorld | urlname=OsculatingCircle | title=Osculating Circle}}): Osculating Circle
- Osculating Curves ({{MathWorld | urlname=OsculatingCurves | title=Osculating Curves}}): Osculating Curves
- Osculating Interpolation ({{MathWorld | urlname=OsculatingInterpolation | title=Osculating Interpolation}}): Osculating Interpolation
- Osculating Plane ({{MathWorld | urlname=OsculatingPlane | title=Osculating Plane}}): Osculating Plane
- Osculating Sphere ({{MathWorld | urlname=OsculatingSphere | title=Osculating Sphere}}): Osculating Sphere
- Oseledec Theorem ({{MathWorld | urlname=OseledecTheorem | title=Oseledec Theorem}}): Oseledec Theorem
- Ostomachion ({{MathWorld | urlname=Ostomachion | title=Ostomachion}}): Ostomachion
- Ostrowski-Hadamard Gap... ({{MathWorld | urlname=Ostrowski-HadamardGapTheorem | title=Ostrowski-Hadamard Gap...}}): Ostrowski-Hadamard Gap...
- Ostrowski's Inequality ({{MathWorld | urlname=OstrowskisInequality | title=Ostrowski's Inequality}}): Ostrowski's Inequality
- Ostrowski's Theorem ({{MathWorld | urlname=OstrowskisTheorem | title=Ostrowski's Theorem}}): Ostrowski's Theorem
- O-Symbol ({{MathWorld | urlname=O-Symbol | title=O-Symbol}}): O-Symbol
- Otter's Theorem ({{MathWorld | urlname=OttersTheorem | title=Otter's Theorem}}): Otter's Theorem
- Ouchi Illusion ({{MathWorld | urlname=OuchiIllusion | title=Ouchi Illusion}}): Ouchi Illusion
- Oudor ({{MathWorld | urlname=Oudor | title=Oudor}}): Oudor
- Oui-Ja Board Curve ({{MathWorld | urlname=Oui-JaBoardCurve | title=Oui-Ja Board Curve}}): Oui-Ja Board Curve
- Outcome ({{MathWorld | urlname=Outcome | title=Outcome}}): Outcome
- Outdegree ({{MathWorld | urlname=Outdegree | title=Outdegree}}): Outdegree
- Outer Automorphism ({{MathWorld | urlname=OuterAutomorphism | title=Outer Automorphism}}): Outer Automorphism
- Outer Automorphism Group ({{MathWorld | urlname=OuterAutomorphismGroup | title=Outer Automorphism Group}}): Outer Automorphism Group
- Outer Inscribed Square... ({{MathWorld | urlname=OuterInscribedSquaresTriangle | title=Outer Inscribed Square...}}): Outer Inscribed Square...
- Outer Napoleon Circle ({{MathWorld | urlname=OuterNapoleonCircle | title=Outer Napoleon Circle}}): Outer Napoleon Circle
- Outer Napoleon Point ({{MathWorld | urlname=OuterNapoleonPoint | title=Outer Napoleon Point}}): Outer Napoleon Point
- Outer Napoleon Triangle ({{MathWorld | urlname=OuterNapoleonTriangle | title=Outer Napoleon Triangle}}): Outer Napoleon Triangle
- Outer Pentagon Point ({{MathWorld | urlname=OuterPentagonPoint | title=Outer Pentagon Point}}): Outer Pentagon Point
- Outer Product ({{MathWorld | urlname=OuterProduct | title=Outer Product}}): Outer Product
- Outer Quermass ({{MathWorld | urlname=OuterQuermass | title=Outer Quermass}}): Outer Quermass
- Outer Soddy Center ({{MathWorld | urlname=OuterSoddyCenter | title=Outer Soddy Center}}): Outer Soddy Center
- Outer Soddy Circle ({{MathWorld | urlname=OuterSoddyCircle | title=Outer Soddy Circle}}): Outer Soddy Circle
- Outer-Totalistic Cellu... ({{MathWorld | urlname=Outer-TotalisticCellularAutomaton | title=Outer-Totalistic Cellu...}}): Outer-Totalistic Cellu...
- Outer Vecten Circle ({{MathWorld | urlname=OuterVectenCircle | title=Outer Vecten Circle}}): Outer Vecten circle
- Outer Vecten Point ({{MathWorld | urlname=OuterVectenPoint | title=Outer Vecten Point}}): Outer Vecten point
- Outer Vecten Triangle ({{MathWorld | urlname=OuterVectenTriangle | title=Outer Vecten Triangle}}): Outer Vecten triangle
- Outlier ({{MathWorld | urlname=Outlier | title=Outlier}}): Outlier
- Outplanar Graph ({{MathWorld | urlname=OutplanarGraph | title=Outplanar Graph}}): Outplanar Graph
- Out-Shuffle ({{MathWorld | urlname=Out-Shuffle | title=Out-Shuffle}}): Out-Shuffle
- Outside ({{MathWorld | urlname=Outside | title=Outside}}): Outside
- Oval ({{MathWorld | urlname=Oval | title=Oval}}): Oval
- Oval of Descartes ({{MathWorld | urlname=OvalofDescartes | title=Oval of Descartes}}): Oval of Descartes
- Ovals of Cassini ({{MathWorld | urlname=OvalsofCassini | title=Ovals of Cassini}}): Ovals of Cassini
- Over ({{MathWorld | urlname=Over | title=Over}}): Over
- Overbar ({{MathWorld | urlname=Overbar | title=Overbar}}): Overbar
- Overcomplete System ({{MathWorld | urlname=OvercompleteSystem | title=Overcomplete System}}): Overcomplete system
- Overdamping ({{MathWorld | urlname=Overdamping | title=Overdamping}}): Overdamping
- Overdot ({{MathWorld | urlname=Overdot | title=Overdot}}): Overdot
- Overhand Knot ({{MathWorld | urlname=OverhandKnot | title=Overhand Knot}}): Overhand knot
- Overlapfree Word ({{MathWorld | urlname=OverlapfreeWord | title=Overlapfree Word}}): Overlapfree word
- Overlapping Rectangles ({{MathWorld | urlname=OverlappingRectangles | title=Overlapping Rectangles}}): Overlapping rectangles
- Overlapping Resonance... ({{MathWorld | urlname=OverlappingResonanceMethod | title=Overlapping Resonance Method}}): Overlapping resonance method
- Overline ({{MathWorld | urlname=Overline | title=Overline}}): Overline
- Oversampling ({{MathWorld | urlname=Oversampling | title=Oversampling}}): Oversampling
- Ovoid ({{MathWorld | urlname=Ovoid | title=Ovoid}}): Ovoid
