A quatrain is a type of stanza or poem that consists of four lines. It often follows a specific rhyme scheme, such as ABAB, AABB, or ABBA. Quatrains are commonly used in various forms of poetry, including sonnets and ballads, and can convey a complete thought or idea within their four lines. Quatrains can be found in the works of many famous poets, such as William Shakespeare and Robert Frost. They are versatile and can express a range of emotions and themes, making them a popular choice for both traditional and contemporary poetry.