The Animation Cancel is a frame-perfect glitch in Dark Souls that allows the placer to cancel the animation of an action caused by interacting with an object, for example opening a door. It requires the player to be staggered by an attack on the exact frame he uses the object, so that the stagger animation takes precedence over the action's animation.
Examples of Animation Cancels
Generally, every animation of an action that is caused by interacting with an object and puts the player into an invinciblity state can be cancelled by this method.
(The following list may not be exhaustive)