So many people I know (or have played chess with) have never heard of En passant and will call me out for cheating.
En passant is a move in chess. It is a special pawn capture that can only occur immediately after a pawn makes a double-step move from its starting square, and it could have been captured by an enemy pawn had it advanced only one square. The opponent captures the just-moved pawn "as it passes" through the first square. The result is the same as if the pawn had advanced only one square and the enemy pawn had captured it normally.
Read more on En passant at Wikipedia
I find that it is overall an uncommon move, I hardly ever have the opportunity to use it.
Why aren't people taught the move when they first learn chess? (I didn't know about it until I'd been playing for multiple years)
Read more on En passant at Wikipedia