A couplet is a pair of lines of verse that form a unit. Most couplets rhyme aa, but this is not a requirement.

Poetry in rhyming couplets is one of the simplest rhyme schemes:

 aa bb cc dd ee ff... etc. 

This scheme was used in Chaucer's The Canterbury Tales in the 14th century and became popular again in the eighteenth century with poets such as Dryden and Alexander Pope. Kurals, which form a subclass of the Venpa class of Tamil poetry, are couplets. Tirukkural is a popular book written in Kural Venpa form. Couplets with a meter of iambic pentameter are called heroic couplets.

Couplets can also play a role in more complex rhyme schemes. For example, Shakespearean sonnets end with a couplet.