Fork
A fork attacks two or more enemy pieces with one piece at the same time, so the opponent cannot save everything. Knights are the classic forking piece because their attack cannot be blocked, only moved away from. The strongest forks include the enemy king: a check must be answered at once, and the second target falls by itself.
The knight on f6 attacks the king on e8 and the queen on d7 at once — Black saves one piece, not both.