Cinquain is an interesting and little-known form. (My spell-checker didn't even recognize it as a word!) It has five lines, which explains its name: origins in the French cinq, for five. It does not rhyme. A basic cinquain:
"Rowboat
On the water:
Fish swim swiftly past.
Where does this stream lead? I don't know.
Do you?"
The first line has two syllables. The second line has four syllables. The third line has five syllables. The fourth line has eight syllables. The fifth line has two syllables.
Other than the basic line- and syllable-counts, the only real rule is that you can't break one word between lines. For example, you couldn't say Fantast/ically.