This is en passant. If a player (say White) moves to the 5th rank with his pawn and the opposing player (Black) has his pawn on the initial square on the 7th (to him the 2nd rank) rank, and moves up two squares, then the first player (White), on his move, has the option of taking that pawn as if it moved up one square. The pawns of the opposing player (Black) must be on either adjacent file, but not in front of the White pawn.
Here is a link on it
http://www.conservativebookstore.com/chess/enpass.htm
I have only been playing Chess about a year now and have become totally fascinated with the game ,although I wish I could be a lot better. Anyhow could someone please explain the "en Passe" move to me or at least that's what I think its called. I read in a chess basics book about the move but I don't understand what they mean in there explanations for the move. It's killing me to know I could be using this move in games but can't because I'm just stupid or something :) ,any help would be greatly appriciated, Thanks.