Villanelle
Lewis Turco, in The Book of Forms, defines the Villanelle as follows:
“The French villanelle, like the terzanelle, is a poem of five triplet stanzas and a concluding quatrain, but it turns on only two rhymes. Lines one and three of triplet one are refrains, the first of which reappears as lines 6, 12, and 18; the second reappears as lines 9, 15, and 19: A1bA2 abA1 abA2 abA1 abA2 abA1A2 or, sometimes, in reverse order:abA2 A1. Every line is the same metrical length.” (Turco, 2020: p. 368)