What is a five line stanza called?

A 5-line stanza of any kind can be called a quintain, a quintet, or a cinquain. However, the word cinquain is also used both for a particular verse form of French origin, and for a particular syllable-counting form (of no great merit or interest, as far as I can see). It is therefore best to stick with quintain as the general word for any 5-line stanza.