A stanza or poem consisting of four lines. In the basic form, Lines 2 and 4 must rhyme while having a similar number of syllables.
A Quatrain is a type of poem which has its lines of verse grouped in four-line stanzas. It is one of the most common stanza forms in English verse, and can be traced back to the ancient literary traditions of Rome, Greece and China. The term quatrain may refer to a single stanza or the entire poem.
There are many forms of quatrain, each featuring variations of line length and rhyme schemes. Some recurring forms have become accepted as conventions and given names.
Among the most common is the ballad stanza, familiar in English verse and song through the centuries. This named form specifies alternating lines of four and three feet in each stanza, and the rhyme is usually A-B-C-B. This quatrain form also appears extensively in hymns. The elegaic, or heroic, quatrain is a structure using four lines of uniform length, the rhythmic stresses of iambic pentameter, and an A-B-A-B rhyme. Or if the rhyme is A-B-B-A, that's an Italian quatrain.