What is the name of the 19-line poetic form with two refrains?

A villanelle is a 19-line poetic form built from five tercets followed by a concluding quatrain, with two recurring refrains.

The form’s pattern is highly organized. The first and third lines of the opening tercet return alternately at the ends of the next four tercets, then appear together in the final quatrain. The poem also uses two repeating rhyme sounds, traditionally arranged around an “a” rhyme and a “b” rhyme.

Despite its strict modern structure, the villanelle began as a loose Italian pastoral song or dance. Its fixed poetic pattern developed later, especially through Jean Passerat’s 1606 poem “Villanelle (J’ay perdu ma Tourterelle).” French poets helped establish the form before it became especially popular in English.

Readers often confuse a villanelle with a rondeau because both use repetition. A rondeau, however, has a different stanza and refrain structure. Dylan Thomas’s “Do not go gentle into that good night” is a famous English-language villanelle.