*dryly* I figured that google exists and one can google it.
Anyhoo, it's a real time (even more real time than IM - you can watch people type! Which is way cool... and sorta annoying at times when people keep effing interrupting you) communication/collaboration tool. It's like google docs+email+im+forums on crack, really. And it makes it insanely easy to share, well, anything.
Mostly I'm using it to spam the Stargatewave. As far as we can tell, the Stargate fandom is the most active fandom (and possesses the largest number of organised waves entirely) on google wave for some crazy reason. We've absolutely murdered the Trekkies for one. Mwahaha.
In all honesty, it is one of those things you need to use to understand. But, well, you can always just watch one of the intro to Wave videos google has posted on YouTube.