As its name suggests, a couplet has two lines. The last word of each line rhymes, and both lines have the same meter. In poetry, meter generally refers to the number of syllables in each line and the way each syllable is accented.
For example:
My English teacher wants me to use imagination
So I go to math class and let my mind go on vacation!
While rhyming is the norm, not all couplets must rhyme to be considered true couplets.
Couplets have to pack a lot of meaning into two short, concentrated lines. Some poets will use a single, two-line approach to make a distinctively profound statement that appears more resonant because of the white space surrounding the lines. Other poets will write several couplets in one poem, with each new couplet relying on the former to add meaning within a short, equally fulfilling space.
Couplets, like poetry, contain varying themes. The subject may be fun or serious, depending on the poet. Maxine Kumin's "Morning Swim" describes a woman's descent into water as a deeply symbolic event:
"Into my empty head there come
a cotton beach, a dock wherefrom
I set out, oily and nude
through mist in oily solitude."
Other couplets, such as Richard Steere's "On a Sea-Storm nigh the Coast," contain epic narrative:
"Wave after Wave in Hills each other Crowds,
As if the Deeps resolv'd to Storm the Clouds."
A sonnet contains 14 lines that include three quatrains, or four-lined stanzas, followed by the final two-lined couplet. When used in sonnets, the role of a couplet is to provide the final reveal of the poem, the thesis or meaning of the story or the turning point in the narrative. Shakespeare is considered to be one the most famous sonnet writers of all time. In sonnet 18, Shakespeare ends with a couplet that sums up the final message of the sonnet:
"So long as men can breathe or eyes can see,
So long lives this, and this gives life to thee."