Why is en passant hardly heard of? 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
It is taught together with the rest of the rules of the game. You playing for years without knowing about it has nothing to do with that, either you learn the rules or you don't, you won't self-discover them no matter how many years you play, specially not when your playing pool is limited solely to your friends who may not know certain rules either. So you not knowing about it doesn't make for a case that it's poorly taught. 

Now chesswise, I think it's quite clear why it's a relatively rare type of move given that it can only be played when there are still pawns at starting position and when moved two squares, constraints make events rare. That said, its potential as a move is still rather frequently employed, for instance to stop your opponent's desired queenside pawn expansion, following is a typical example:

 [Title "En passant being employed"]
 [fen "r1bq1rk1/pp1nbppp/4pn2/2pp4/P2P1B2/2P1PN2/1P2BPPP/RN1Q1RK1 b - - 0 8"]

 1...a6 2.a5 b5 (2...b6 3.axb6) 3.axb6


Black plays a6 to prepare b5 and their desired setup is to have the a6-b5 pawns which provides important light-square control and creates space on Black's queenside. White on the other hand, prevents it by simply playing a5, with the underlying tactical idea being to capture with en passant in case black tries to expand with b5. If black did play it regardless, then after white takes, black's left with a weakened a6 pawn. So with a5 we stop both b6 and b5 for good.