In ice hockey, a tripping penalty is when a player uses his stick, skates, or any other part of his body to trip an opponent. This can be done deliberately or accidentally. If done deliberately, it is usually a minor or major penalty (the referee decides which one it is), but if done accidentally, it is usually just a two-minute minor penalty.
There are some exceptions to this rule. For example, if a player trips an opponent who then falls into the goaltender and prevents him from making a save, the tripping player will receive a penalty shot. On the other hand, if a player trips an opponent who was about to shoot the puck at the net and the shot is prevented as a result, no penalty will be given because the play was stopped before it had a chance to develop.
So there you have it! That's what a tripping penalty is in ice hockey.