A couplet is a pair of 2 poetry lines have the same meter. The word "Couplet" comes from a French word meaning "two pieces put together." The first time the term was used in poetry was in Sir P. Sidney's Arcadia in 1590. Although couplets traditionally rhyme, not all do. Rhyming couplets are one of the simplest forms of poetry.
True wit is nature to advantage dress'd;
What oft was thought, but ne'er so well express'd.
Whether or not we find what we are seeking
Is idle, biologically speaking.
Edna St. Vincent Millay