Flattery (also called adulation or blandishment) is the act of giving excessive compliments, generally for the purpose of ingratiating oneself with the subject. It is used in pick-up lines when attempting to initiate romantic courtship.
Historically, flattery has been used as a standard form of discourse when addressing a king or queen. In the Renaissance, it was a common practice among writers to flatter the reigning monarch, as Edmund Spenser flattered Queen Elizabeth I in The Faerie Queene, William Shakespeare flattered King James I in Macbeth and Niccolò Machiavelli flattered Lorenzo II de' Medici in The Prince.
Most associations with flattery, however, are negative. Negative descriptions of flattery range at least as far back in history as The Bible. In the Divine Comedy, Dante depicts flatterers wading in human excrement, stating that their words were the equivalent of excrement, in the second bolgia of 8th Circle of Hell.
Historians and philosophers have paid attention to flattery as a problem in ethics and politics. Plutarch wrote an essay on "How to Tell a Flatterer from a Friend." Julius Caesar was notorious for his flattery. In his Praise of Folly, Erasmus commended flattery because it "raises downcast spirits, comforts the sad, rouses the apathetic, stirs up the stolid, cheers the sick, restrains the headstrong, brings lovers together and keeps them united." 
"To flatter" is also used to refer to artwork or clothing that makes the subject or wearer appear more attractive, as in:
- The king was pleased with the portrait, as it was very flattering of his girth.
- I think I'll wear the green dress because it flatters my legs.
- Regier, Willis Goth. In Praise of Flattery (Lincoln: University of Nebraska Press, 2007).