Yes, Pokemon A is faster than Pokemon B, but A is paralyzed, so B trumps the speed stat difference and goes first.
Yes, you used your ultimate combo in blah blah fighting game, but it connected while my character was in an i-frame (invincibility frame), so that trumps it.
Its basically any time something either totally negates, or overpowers some other effect or attack or system.
Its often associated with a last ditch saving move reserved until its needed, but it does not have to be.