Poems can be described and categorized according to features that characterize similar and related lines, such as stanza structure and rhyme scheme. One way to define poetic structure is based on a count of the number of lines that are rhythmically and structurally related, such as the couplet (having two similar and related lines), or the triplet, which features three lines.
Features of the Triplet
Poetic structure can include sets of two lines (couplets), three (triplets) and four or more (the quatrain and beyond). These lines are grouped based on similar metric and rhythmic structures and may be connected to another set by rhyme scheme or metrical structure. A set of three lines connected in this way is called a triplet.
Triplets and Rhyme Scheme
One feature that identifies a triplet can be a rhyme scheme such as AAA, in which all three triplet lines rhyme, as in Shakespeare's "The Phoenix and the Turtle:" "Truth may seem, but cannot be;/Beauty brag, but 'tis not she;/Truth and beauty buried be." Rhyme schemes can cross stanzas, so a triplet may share a rhyme scheme such as ABAB with another triplet set. In unrhymed poetry such as free verse, other features can connect triplets, such as repetitions in meter or sound patterns.
Triplets and Stanzas
A stanza in poetry is a set of lines related structurally and thematically. A triplet can be part of a larger poetic structure such as in Wallace Stevens' "Disillusionment at 10 O'Clock:" "None are green,/Or purple with green rings,/Or green with yellow rings,/Or yellow with blue rings ... " It may also stand alone as a stanza in itself, as in Stevens' "The Snow Man:" "One must have a mind of winter/To regard the frost and the boughs/Of the pine tree crusted with snow."
Triplets and Tercets
A poem consisting solely of the three related lines of a triplet is called a tercet. Although the term tercet refers to poetry in the Western traditions, other types also exist, such as the haiku, which consists of three thematically related lines. Some poetic forms such as the sestina, a fixed form poem constructed around a set of repeating keywords, require a tercet as part of the poem's overall pattern.