The dizzy state, where your character takes one hit too many and is off in la-la land, needing a little time to screw their head back on. This is called “stun” in Japanese, as well as by many English players, but this is not what this article is talking about.
A “stun” is a state in which you are unable to move. This can refer to plenty of such occasions: from the time after you use a move and are returning to a more neutral state (recovery) and the opponent’s time spent in the resulting pushback (called “hit stun” or “hitstun” by many) or time spent blocking it (“block stun” or just “blockstun”), to even game-specific penalties like the time forcibly spent landing from a jump (see landing cancel) or after stopping a dash.
Using language properly, “stun time” should be used to refer to the time period in which this happens, and “stun” should refer to the state itself. Unfortunately, as with much game lingo, grammar often goes right out the window. Use discretion when referring to any “stun” term, lest you cause confusion; the variety of situations to which it could apply makes this an unfortunate reality.