It's an RPG played with a pen and paper, dice, and, sometimes a game board and game pieces and NOT a computer.
That's about it.
By the way,
Would anyone want to play a P&P RPG over the internet? It shouldn't be that hard to do. As long as we have a dedicated DM with the right pieces, online character sheets (can be scanned), and an instant messaging system that provides video or image support.
That or... you know, the forum. It'd be a much longer game, and the players will have to be a lot more dedicated as well though.
I'd consider hosting a game of that Mouse Guard thing if I find a discount copy.