In and of itself, a quatrain is simply four lines written together.  The KIND of poem it is determines what the meter is, if any at all.  

So such a poem could be a free verse quatrain, or four lines in iambic pentameter, or four lines of various meter that rhyme with some kind of rhyme scheme, or four lines that merely have internal or hidden rhyme...

in a word, ANY collection of thoughts so long as it's in  four lines... at least so far as I know.

Remember that quatrain may merely mean four lines within a poem...

or a poem of four lines.  The example I give is a poem of four lines.

hopin' that sLightly clears up your questions, Daniel  8)

Quatrain

A quatrain is either a poem or any section of a poem that has four lines, whether metrical, rhyming or free verse.

A simple example as a simple reminder:




Translation:

Short Line

this train
has four
(rail) cars
that's all