Educate Me: Mise en scene

So, I've decided that there's one thing I can't really get my head around, as a critical concept (I admit there's lots of things I can't get my head around - poles for instant - not flexible enough) - a term I see used all the time, but I have to be honest I've never seen it used the same way twice.

It's a term people throw out in reviews ALL the time as well (well, proper smart film critics do at least). That term is:

MISE EN SCENE (yes I got rid of the stupid ` over the e, get over it)

I get that it's a sort of collection of all that goes into a shot, but I see it used so sporadically, and ill explained I wanted to ask any of my readers out there:

Can you explain it to me in some sort of defined way (Wikipedia is unreliable but if that's close enough let me know)?

I'd appreciate it :)