Foil

Foil may refer to:

Materials

• Foil (metal), a quite thin sheet of metal, usually manufactured with a rolling mill machine
• Metal leaf, a very thin sheet of decorative metal
• Aluminium foil, a type of wrapping for food
• Tin foil, metal foil made of tin, the direct predecessor to aluminium foil
• Transparency (projection), a thin sheet of transparent flexible material, placed on an overhead projector for display to an audience

Fluid dynamics

• Foil (fluid mechanics)
  • Airfoil, a foil operating in air
  • Hydrofoil, a foil operating in water
  • Parafoil, a non-rigid airfoil, inflated during use
• Foil bearing, a type of fluid bearing

Arts and culture

• Foil (architecture), decorative device derived from cusps of circles
• Foil stamping, a printmaking technique
• Foil (fencing), one of the three weapons used in modern fencing
• Foil (fiction), a subsidiary character who emphasizes the traits of a main character
  • Comedic or comic foil, the straight man in a comedy double act
• "Foil" (song), "Weird Al" Yankovic's parody of Lorde's song "Royals"

Navigation

• Hydrofoil, a type of high-powered motorboat that uses underwater foils to lift its hull above the water when moving at high speeds
• Bruce foil, a foil used on an outrigger to prevent a boat from heeling
• Centreboard, a movable keel that functions as a foil
• Foilboard, a surfboard using a hydrofoil

Other uses

• People in a police lineup
• First-order inductive learner – a rule-based learning algorithm
• The FOIL method, a mnemonic in algebra, to expand the product of two first-degree polynomials ("linear factors")
• FOIL (programming language), either of two now-defunct computer programming languages
• Forum of Indian Leftists, a political group of Indian intellectuals
• Freedom of information legislation or Freedom of Information Law (FOIL)
• Ultrasonic foil (papermaking), a type of high-frequency vibrating foil involved in papermaking
• Split tally, in ancient financial accounting, the part of a split tally stick given to the recipient in a transaction