What is a couplet in a poem mean?
A couplet is generally used in poetry. As indicated in the term so similar to "couple," it refers to two lines paired together, and in poetry these lines rhyme.
For example, in Shakespearean (aka Elizabethan) sonnets, the last two lines of this 14-line poem rhyme. The author will many times use these two lines at the end of the sonnet to summarize the ideas presented in the first 12 lines, so that the rhyming couplet may act much the way a conclusion would in an essay.
The rhyming of the couplet occurs at the end of the first line, coinciding with the sound at the end of the following line (called "end rhyme"). It can be a perfect rhyme (such as "car" and "far") or a near rhyme (such as "car" and "fair").
For an example, search William Shakespeare's Sonnet #29, which begins, "When in disgrace with fortune and men's eyes..." The last two lines are examples of a rhyming couplet. After reading this "poem," you hear the pleasant chord of the rhyme, but you will also see the power with which Shakespeare drives his final point home. It's really beautiful, and surprisingly so, made up of only two lines that rhyme!
A couplet in poetry refers to two consecutive lines (meaning, two lines in a row) that have the same meter, usually rhyme at the end, and form a single unit when together.
Chaucer's Canterbury Tales are written almost exclusively in rhyming couplets. Simple in form, easy to write, remember, and even guess at, today - rhyming couplets are most often associated with children's nursery rhymes, Dr. Seuss, or other somewhat silly lyrics. The reason is that rhyming couplets often sound very sing-songy, making them especially appealing to children. Very few notable poets have mastered the rhyming couplet at an adult level (Alexander Pope comes to mind).
Chaucer likely was using the rhyming couplet exactly for its sing-songy effect when he used it in The Canterbury Tales. The tales themselves are written in a fashion very similar to nursery rhymes and fairy tales - and clearly Chaucer wanted to take serious subjects (characters included) and make fun of them by painting them in a more childish light.