A villanelle is a structured form of poetry consisting of 19 lines, divided into five tercets followed by a quatrain. It features a specific rhyme scheme of ABA for the tercets and ABAA for the quatrain. The first and third lines of the opening tercet are repeated alternately at the end of the subsequent stanzas and are both included in the final quatrain. This poetic form is known for its musical quality and emotional depth, often exploring themes of love, loss, and longing. A famous example of a villanelle is Dylan Thomas's "Do Not Go Gentle into That Good Night," which showcases the form's unique repetition and rhythm.