The rondel is a French verse form. It consists of 13 lines in 3 stanzas and contains two refrains (repeated lines). The rhyme scheme is below. The uppercase letters represent the refrains.
A B b a
a b A B
a b b a A
Rondels are usually written in lines of 8 syllables.
The Poetry Foundation defines it a bit differently. Here is their definition.
A poetic form of 11 to 14 lines consisting of two rhymes and the repetition of the first two lines in the middle of the poem and at its end. Algernon Charles Swinburne’s poem entitled The Roundel is 11 lines in two stanzas.
Whichever form you use, I hope you will join me this week in writing a rondel. Please share a link to your poem or the poem itself in the comments.