Most skills have an activation time during which the character is using the skill. During this activation time, it is possible to cancel a skill by pressing a movement key. The "Cancel Action" hotkey can also be used to cancel your skill and is usually faster and more reliable.
Canceling has the following results:
This can be especially useful when you know you are going to be interrupted, when skills such as Diversion are used against you, or when you simply push the wrong button.