The top shot really is a wasted shot. It happens when you hit on top of the golf ball rather than striking it correctly at the base of the ball.
Golfers tend to top shots when they get too intent on hitting the golf ball and forget to swing the golf club freely. That means their swing stops at the ball rather than continuing through to a full finish.
A simple drill to encourage you to reach a good finish position is to set up to the ball but rather than make a backswing simply push off the back foot to swing through to a finish.
Watch this video instruction tip to see how to avoid the topped shot.