A quatrain is a type of stanza, or a complete poem, consisting of four lines.
Existing in various forms, the quatrain appears in poems from the poetic traditions of various ancient civilizations including Ancient Greece, Ancient Rome, and China; and, continues into the 21st century, where it is seen in works published in many languages. During Europe's Dark Ages, in the Middle East and especially Iran, polymath poets such as Omar Khayyam continued to popularize this form of poetry, also known as Ruba'i, well beyond their borders and time. There are twelve possible rhyme schemes, but the most traditional and common are: AAAA, AABB, and ABAB.
The Ruba'i form of rhymed quatrain was favored by Omar Khayyám, among others. This work was a major inspiration for Edward FitzGerald'sRubaiyat of Omar Khayyam, written in Persian. The ruba'i was a particularly widespread verse form: the form rubaiyat reflects the plural. One of FitzGerald's verses may serve to illustrate:
Come, fill the Cup, and in the fire of Spring
Your Winter garment of Repentance fling:
The Bird of Time has but a little way
To flutter—and the Bird is on the Wing.
The Midnight Songs poetry form is from Fourth Century China, consisting of regular five-character lines, with each quatrain formed from a pair of rhymed couplets. The subject matter involves the personal thoughts and feelings of a courtesan during the four seasons, into which the quatrains are individually assigned.
The Shichigon-zekku form used in Classical Chinese poetry and Japanese poetry. This type of quatrain uses a seven characters length of line. Both rhyme and rhythm are key elements, although the former is not restricted to falling at the end of the phrase.
Ballad meter (The examples from "The Unquiet Grave" and "The Wife of Usher's Well" are both examples of ballad meter.)