A couplet consists of two lines of poetry, generally rhymed at the end and establishing their own structure and ideas. In their closed form each line is end-stopped, meaning each carries its own meaning while in the open form the meaning of one line continues to the other.
In English poetry, the model couplet is called heroic. This form has two rhymed lines of iambic pentameter meter (10 syllables) in each line. Geoffrey Chaucer laid out the form in the 14th century, but the form was brought to its artistic pitch by John Dryden and Alexander Pope in the late 1600s to the early 1700s.The last two lines of the English sonnet use this form.
French narrative poetry used the alexandrine, a line of 12 syllables (iambic hexameter), as its primary form of couplet, influencing 17th and 18th century German and Dutch poets. Alexandrines were used at the ends of stanzas and were called codas. French poets also used the word couplet to describe a stanza. They employ, for example, a "square" couplet, comprising eight lines, each line having eight syllables.
Other forms include the short couplet, formed with iambic or trochaic tetrameter (eight syllables per line); the split couplet with a first line of iambic pentameter and a second in iambic dimeter (four syllables) and the qasida, an Arabic form that can have a number of lines containing the same rhyme.