A couplet is a type of poem that contains pairs of lines that are of the same length and have the same rhythmic structure, which is known in poetry as meter. The rhyming words in a couplet are typically placed as the last word of each line.
It is not mandatory for the pair of lines to have rhyme scheme at all, as it is common for them to be used as a space filler between lines that do rhyme. The lines can be written in succession of one another or have a line or two placed in between them that does not have the same rhyme structure. A couplet can be written in a formal tone which signals there is a pause at the end of each line indicating the end of a phrase, or as a run on which uses the two lines to finish one continuous thought.