Final answer:
A couplet is a pair of rhyming lines with identical meter, often used to conclude sonnets. Couplets can also come in variations like the split couplet, which have different meters for each line. They are distinct from tercets, quatrains, and other stanzas.
Step-by-step explanation:
When discussing poetry, two lines that usually rhyme and have identical meter are referred to as a couplet. A couplet consists of two adjoining lines that share an end rhyme and commonly the same meter. This stands in contrast to other stanza forms such as a tercet (a three-line stanza), a quatrain (a four-line stanza), or a sonnet which typically has fourteen lines and often utilizes couplets at the end. The poetic device of end rhyme, stressed syllables at the ends of verse lines, and meter, the regular pattern of stressed and unstressed syllables in a line of poetry, are important aspects of couplets.
For example, in Shakespeare's Sonnet 18, the couplet at the end serves to summarize and conclude the sonnet's theme. A classic example of a couplet from Alexander Pope's "Essay of Criticism" uses the rhyme scheme AA, demonstrating how couplets have been employed historically. Moreover, a split couplet is a variation which features two rhymed lines with different meters, typically iambic tetrameter and iambic dimeter.