A baseball term.
A foul tip is called when the hitter grazes the ball with the bat so slightly that the ball continues straight back, into the catcher's mitt. So long as the catcher catches the ball, it is considered a foul tip, which is in turn considered a strike. If the catcher does not catch the ball, it is a foul ball (and therefore not a strike if the batter already has two strikes).
It can be very difficult to identify a foul tip if you are not near enough to hear the impact of ball on bat.