Many games use attack animations. Typically, animations must complete before the next action can be taken. Animation canceling is when an animation does not block the next action.
Generally, one cancels an animation after the ability has produced its effect in order to avoid waiting. Occasionally, one cancels an animation before the effect in order to do something else better with the time.
- In Bayonetta, it is possible to cancel any attack at any time into a dodge. This encourages a playstyle where all incoming attacks are avoided.
- In Mass Effect 3, the Claymore is a one-shot shotgun that takes a long time to reload, but it is reloaded pretty early in the animation. The reload animation can't be canceled by shooting, but it can be canceled by ducking into cover or using a power. The advantage of canceling the animation is that the overall shooting rate is improved, which improves the damage per second.
In Blade And Soul, animation canceling allows faster attacks. This can lead directly to more damage, or generate resources faster which allows bigger attacks. These resources can also lead to better crowd control/stuns.
In this video, the kung-fu master (KFM) is canceling Straight Jab and Swift Strike into each other with the idea to generate crits and chi to allow the use of Cyclone kick.
At about 1:10, the non-canceling speed is shown. The rest of the time, canceling!
A bit of jargon: 2 and F are the abilities bound to those keys. R is the ability bound to the R key as well as the left mouse button. 2R2RF means to use those keys in sequence.
Most animation canceling is done with R - don't forget: same as left mouse button.
All classes can benefit from animation canceling.