Foul tip

From BR Bullpen

A foul tip is a foul ball whose trajectory is barely affected by a glancing touch from the batter's bat. The rules pertaining to foul tips vary somewhat from those for other foul balls: a foul tip caught on the fly by the catcher is treated as a regular pitch that has been swung at and missed; the batter is not out unless the pitch constitutes the third strike. It is also legal to steal a base on a foul tip that is caught on the fly. However, if the foul tip touches the ground, it becomes a regular foul ball: the ball is dead and baserunners must return to their original bases.

Foul tips can be quite dangerous, as the ball is barely slowed by contact with the bat, but its trajectory can be changed enough to miss the catcher's glove and hit the catcher or umpire full on.

A foul tip becomes a foul ball when it is deviated higher than the batter's head, or outside the reach of the catcher to one side or another of home plate.