Pointer Cancellation
For functionality operated with a single pointer, the down-event is not used to trigger the action unless it's essential — instead, the action completes on the up-event and can be aborted or undone, or the up-event reverses the effect of the down-event.
In plain language
An action (like a button click) shouldn't happen the instant you press down — it should only complete when you release, so you have a chance to change your mind by moving away before letting go.
Why it matters
People with hand tremors or limited motor control can trigger a button by accident just by touching the screen or clicking down. If the action fires immediately on press, there's no way to cancel a mistaken touch.
In practice
Fails this criterion
A "Delete" button deletes the item the instant it's pressed down, with no chance to slide away and cancel before releasing.
Meets this criterion
The same button only deletes the item when the mouse or finger is released while still over the button — sliding away before releasing cancels the action safely.
Test it yourself
Press down on a button or link and, before releasing, drag your finger or cursor away from it. Does the action still happen? If so, this criterion is failing.