A foul tip is a type of putout in which the batter hits the ball sharply backwards towards the catcher, and the catcher is able to catch the ball before it hits the ground or touches anything else. A successful foul tip results in a strike in the count for the batter. If it is not legally caught, then it will simply count as a ball.
A foul tip differs from a foul ball-which if caught results in an out-in that when the ball is hit it must immediately and sharply go straight back towards the catcher. If it pops upwards and back and spends time in the air, it is considered a foul ball.