The first letter of each line of an acrostic forms a word when you read the letters downward. A very complicated acrostic would have the last letter of each line forming a separate word as you read downward, also. Onomatopoeia is the imitation of natural sounds in word form. Find at least five examples of onomatopoeia in a newspaper's comic strip section. When the weather is hot I sleep on a cot.
Quatrains follow couplets.
The first two lines rhyme and the third and fourth lines rhyme. 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.