It means that you are using two lines that rhyme with each other to make one line of poetry. A couplet is a phenomenon When two lines rhyme: For Example; He's no oil painter but he's my delight. All of the girls want him on the first night.If you read those lines aloud, they should rhyme which means that they are a couplet. The couplet rhyming is often used to create rhythm and flow in poetry.