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.
Other types of tercet include an enclosed tercet where the lines rhyme in an a b a pattern and terza rima where the a b a pattern of a verse is continued in the next verse by making the outer lines of the next stanza rhyme with the central line of the preceding stanza, b c b, as in the terza rima or terzina form of Dante Alighieri's Divine Comedy. There has been much investigation of the possible sources of the Dantesque terzina, which Benedetto Croce characterised as "linked, enclosed, disciplined, vehement and yet calm". William Baer observes of the tercets of terza rima, "These interlocking rhymes tend to pull the listener's attention forward in a continuous flow.... Given this natural tendency to glide forward, terza rima is especially well-suited to narration and description".
A tercet may also form the separate halves of the ending sestet in a Petrarchan sonnet, where the rhyme scheme is abbaabba cdccdc, as in Longfellow's "Cross of Snow". For example, while "Cross of Snow" is indeed a Petrarchan sonnet, it does not follow the form of abbaabba cdccdc. Instead, its form is abba cddc efg efg. A tercet also ends sestinas where the keywords of the lines before are repeated in a highly ordered form.