Couplet

A couplet consists of two lines of verse that rhyme with each other, and which have the same meter. Rhyme means that the last sounds in each line possess a certain aural consonance, like the one between the words them and gem. Meter means the lines have the same pattern of stressed and unstressed syllables. The couplet has been important to poetry historically, although it is perhaps become less significant within modern prose or poetry.  

Definition of couplet

A couplet (as its name suggests) refers to two lines of poetry that are related to each other in a certain way. Usually, a the two lines of the couplet have the same meter, and they rhyme with each other. (So, the two phrases "have the same meter" and "rhyme with each other" would almost qualify as an accidental couplet.)

How to use in literature

Here are a few sentences, for your reference, in which the literary term couplet is being used in a correct way. Here are a few more couplet examples:

"The man, upon realizing that his friend was speaking a couplet every other sentence, began to wonder whether this was being done on purpose, or whether he was just imagining things." 

"The man wanted to create a clever couplet for his own tombstone, but he was having trouble finding a good rhyme."

"One one of Nabokov's most famous novel, there a section that is constructed entirely on the basis of the poetic form known as the heroic couplet." 

In case you are still a little confused about the meaning of the literary term couplet, here are a few basic rules that can clarify the matter for you. 

1. The couplet is generally only found in poetry. Beautiful or melodic prose may sometimes contain lines that seem to form a couplet; but if even if this is the case, people would not usually call the pairing a couplet per se. Among other things, prose writing may contain phrases that seem like a couplet but that are a little less intentional and/or formally precise. 
2. The two main elements of the couplet are rhyme and meter. Rhyme refers to a matching of the sounds of the last words of each line of the couplet. Meter refers to the rhythm of the stressed and unstressed syllables in the couplet. A common meter in English poetry, for example, is iambic pentameter: a set of ten syllables with an unstressed/stressed rhythmic pattern. 

Other uses of couplet

Historically, poetry was expected to follow somewhat strict rules, especially when it come to rhyme and meter. Within this context, the couplet was a very important structure of a lot of poetic forms. For example, the sonnet is a classic example of a form in which the poet is expected to follow specific rules of rhyme and meter; and the couplet thus becomes an essential construction within the sonnet as a whole. Indeed, if any given couplet cannot be found in the right places within the poem, the sonnet could not properly be called a sonnet. 

The couplet has become much less important, however, with the rise of modern poetry. This is because modern poetry has largely seen the rise of free verse: patterns of words that are poetic in their sounds and flow but do not necessarily adhere to any strict guidelines regarding rhyme and meter.

In a way, then, modern poetry tends to resemble lyrical prose; and while the couplet may still be found here and there, it is not as fundamentally important to the structure of the poem as it used to be. On the other hand, a modern poet who does use the couplet thereby evokes a kind of old-fashioned or traditional feeling by doing so.