I've been out of magic for some time, and I'm unfamiliar with some of the terms I've seen mentioned on the forums (e.g. 'Legacy') is there somewhere where such terms, and their meanings, are listed?

The wiki has a lot of these. http://wiki.mtgsalvation.com/article/List_of_Magic_slang

You can search for a lot of stuff there and educate yourself. It's pretty useful. I used it when I got back in at RTR. I didn't know jund or naya, or bant. You'll get it though :)

Thanks, that's helpful.

One term I don't see defined there, though, is...

"Legacy"!

http://www.wizards.com/magic/magazine/article.aspx?x=judge/resources/sfrlegacy

It's just another format with it's own card base. This is the one with all the older cards are allowed to be played. Though for competitive play you'll see some pretty expensive decks.