Tercet

A tercet is composed of three lines of poetry, forming a stanza or a complete poem.

English-language haiku is an example of an unrhymed tercet poem. A poetic triplet is a tercet in which all three lines follow the same rhyme, a a a; triplets are rather rare; they are more customarily used sparingly in verse of heroic couplets or other couplet verse, to add extraordinary emphasis.