This card is extremely elegant from a flavor perspective. It works on a few levels:
Level 1: It's a chess thing! Reina has a chess theme! Perfect.
Level 2: En passant is French for "in passing". So of course it works on passed ICE.
Level 3: En passant is a special chess move that allows you to capture a pawn. It gets a piece off the board. This card gets an ICE off the board.
Level 4: Pawns usually plod forth one space at a time (just like the program of the same name). But they have a special ability where the first time they move, they can move forward two paces. Without the en passant rule, this would allow a pawn to avoid an interaction with an opposing pawn. Even though the pawn moved two, the en passant rule lets the opponent capure the pawn as if it moved one.
For clarification, there's a nice animation showing a white pawn capturing a black pawn here.
What does this have to do with the mechanics of Android: Netrunner? I will tell you. When a runner approaches a piece of ICE, the corp has the choice to rez it, and have the runner encounter it, or not rez it, and then the runner does not encounter it. Not rezzing it is avoiding confrontation.
En Passant, the card, allows the runner to interact with an opposing card after the corp opted to avoid a confrontation.
If we do, think of me, because I will be excited.