Annihilation

When opposing pieces both move to the same destination square they capture each other in what is called an annihilation.

For a pawn this is an alternate way of capturing a piece that isn't on a diagonal.

Try to move the e2 pawn to e4. The e5 pawn will move forward and annihilate with the white pawn.

Notice that for pawns they can annihilate by moving normally or during en passant.

Firstly move the b4 pawn to b5. Black's a7 pawn will have just moved. Then perform an en passant to a6 and annihilate with black's rook that will also move. This is a double capture.