The kyrielle is a French four-line stanza form that has a refrain in the fourth line. Often, there is a rhyme scheme in the poem consisting of the following possibilities:
The poem can be as long as you wish and as short as two stanzas (otherwise, the refrain is not really a refrain, is it?), and, as with many French forms, it is very nice for stretching your poetic muscles.
Also, tres importante! Your lines must contain 8 syllables. I've written an example below to show how this poem works (on a technical level).
"She's not a Pretty Singer"
Evening cell phone conversation--
he rakes his hair with long fingers
that were once filled with devotion,
though she's not a pretty singer.
He never was a man to say,
"baby," or let his eyes linger,
and she only likes boys who stay,
but she's not a pretty singer.
So he offered his warm coat to
another to start a fling her
aging looks could never undo,
and she's not a pretty singer.
Some say she moved to another
state and made her name selling or
buying something, though why bother
when she's not a pretty singer?
Here are some other resources on the kyrielle form: