em-passent

can anybody tell me whats em-passent move?
www.chesskids.com/kids/enpas.htm it is explained in detail here...its basically the EN PASSANT capture happens when a pawn captures a pawn as it PASSES a square.

Hi Vakshayaa ( you are very pretty!)
The question is why the en passant move in modern chess? As for the rules of en passant; Remember that it only happens according to the following rules:
1. A pawn sitting on a 4th rank square for White; or the 5th rank for Black --obviously, these pawns are there for a reason (guarding/watching over a square on the 3rd rank for White or the 6th rank for Black) -- When the Player to move, decides to move a pawn two squares from her 2nd rank for White or 7th rank for Black; her opponent can capture the pawn en passant as if the pawn actually moved one square instead of two. Now, this rule is very interesting! Could it be a remnant of when pawns were only allowed to move one square only before the invention of the modern game?
2. You must capture the pawn immediately; you can't make another move and then next decide to capture the pawn ( I've played some beginners who'd do just that!) Also, there's no en passant on other squares, which again is not clear to many beginners ( yes, I've had players attempt to capture a pawn en passant say, a pawn sitting on the 6th rank vs. a pawn sitting on the 7th.
Good Luck
can anybody tell me whats em-passent move?