This is for all you poets out there. The novelists seeking publication can skip the next paragraph and instead go to this link on how to write a really good QUERY letter.
A QUATRAIN is a stanza of four lines. The possible rhyme schemes vary from an unrhymed QUATRAIN to almost any arrangement of one-rhyme, two-rhyme, or three-rhyme lines. Perhaps the most common form is the abab sequence; other popular rhyme patterns are aabb; abba; aaba; abcb. Robert Frost's "In a Disused Graveyard" consists of four QUATRAINS. In iambic tetrameter, each in a different rhyme scheme: abba, aaaa, aabb, abab-- quite a tour de force. W. H. Auden's "Leap Before You Look" rhymes abab bbaa baab abba aabb baba, in effect turning itself inside out.
(This post has been inspired by and in some instances, directly quoted from A Handbook to Literature, 8th Edition, by William Harmon and C. Hugh Holman)