Here's a famous quatrain. They contain a couplet and a triplet. Limericks are meant to be funny. Free Verse , lets the writer decide how the poem should look, feel and sound. It lets writers freely express their feelings.
Rap is a mix of most of the above.
Sometimes it rhymes, sometimes not. It may contain couplets and triplets. Some of it is free form. And it has a beat. Students may have fun creating some rap rhymes.