One of the most difficult and complex of the various French forms, the sestina is a poem consisting of six sixline stanzas and a threeline envoy. It makes no use of the refrain. This form is usually unrhymed, the effect of rhyme being taken over by a fixed pattern of endwords which demands that these endwords in each stanza be the same, though arranged in a different sequence each time.

Website: http://www.writing.upenn.edu/~afilreis/88/sestina.html