Final answer:
A quatrain is a four-line stanza in poetry, not to be confused with a couplet which has two lines, or a tercet which has three lines.
Step-by-step explanation:
A quatrain refers to a four-line stanza in poetry. This structure is one of the most common stanzas found in poetry, with various rhyme schemes such as AABB, ABBA, AABA, and ABCB. One of the famous examples illustrating a quatrain’s structure is seen in Samuel Taylor Coleridge's "The Rime of the Ancient Mariner." In contrast, a couplet refers to a two-line stanza, and a tercet or triplet is a three-line stanza. When discussing stanzas within poetry, identifying the length and organization of lines is crucial for understanding the form and pattern of the poem.