Fork

To fork is to use one piece to attack two or more of your opponent's pieces at the same time.

In this example the white pawn places the black king in check. Since the white bishop is guarding square h7 and the white king is guarding squares g5, g6 and g7 the only thing that the black king can do is move to h5. The white bishop then moves to e2, putting the king and black rook in fork. The only choice that black has at this point is to move the king out of check and the white bishop captures the black rook!