what is a cinquain?

Answer 1

In poetry, a cinquain or quintain is a 5 line stanza, varied in rhyme and line, usually with the rhyme scheme ababb. An example of cinquain is the following stanza from Robert Browning's poem "Porphyria's Lover":

Murmuring how she loved me -- she
Too weak, for all her heart endeavour,
To set its struggling passion free
From pride, and vainer ties dissever,
And give herself to me for ever.

Answer 2

One more than a quatrain, of course.

It's a kind of American haiku, with unrhymed five verses.