A position in which the cue ball cannot hit any legal object ball directly is called a snooker.
The term describes the layout of the balls rather than a particular stroke. A player may be snookered when another ball blocks the direct path from the cue ball to every legal target. The player must then attempt a cushion escape, often using sidespin, pace and one or more cushions.
Being snookered can create a major tactical advantage because an unsuccessful escape may give the opponent points through a foul. In official play, the referee determines whether a direct path exists and whether the player has hit the ball on.
“Safety” is different: it describes a tactical shot intended to leave the opponent in difficulty. A safety may produce a snooker, but the two terms are not interchangeable.