In a melee attack, you can follow up with an additional powerful kick, having a chance of stunning your opponent. This is especially true if you're wearing combat boots.
On success you do 11 bludgeoning damage and 25% chance to stun on hit for 2.5 rounds.
Abilities are associated with one or more classes and can be used by both players and NPCs, and most abilities has to be learned and sometimes require points to be invested into them. Rarely, you can find a special ability scroll with limited uses, and these can be used if you have not learned the ability, but with a limited number of uses on the scroll.