A couplet is a stanza (or even a poem) consisting of two lines. These need not rhyme, nor be the same length, but can be. If there is no enjambment at the end of the second line, it can be called a closed couplet (the opposite being an open couplet), especially if this is a recurring pattern. A closed rhyming couplet in iambic pentameter, especially one which forms a unit of sense, is called a heroic couplet; many of these can be found in Pope's 'Essay on Man'. It is also possible to find a longer poem whose lines are rhymed in pairs - aabbcc
etc - described as being in rhyming couplets, even if the stanzas are longer than two lines.
Elaine Feinstein's 'Urban Lyric' has an individual aspect of the scene in each couplet, each of which is linked, however, to the adjacent aspects.