being in any position where your opponent is stunned and you are not, or being in a position where you can act faster with a better option than your opponent generally can. being in shield puts you in a terrible position framewise, because unless you can shine/nair (and i mean a good one) out of shield, options are tough to come by in a quick manner.
falco's lasers can either put you in stun while he approaches, or put you in shield while he approaches. powershielding allows a defender to stay in a relatively neutral frame game, and potentially can put the frame advantage in their hands, but a fearful/careful falco can get around such things.
holding frame advantage is one reason why some people, no matter what character, will jab on shield. it will catch people trying to get back to a neutral frame game when they get out of shield, and instead they get jabbed for trying it. the ledgegame is usually advantage to the person on stage. the person on the ledge has to fight back to get to neutral frames, but if you understand their options, such things can be prevented.
it's just an alternate way of looking at the game. you can either look at it in space, look at it through time, or look at it in the full realm of the game as the entire space-time continuum of a match.
most tend to look at it through space though. it's the easier to make sense of, as it's more concrete.
edit: i could also be high. but looking at things in this manner makes sense to me, and i feel it's worth a discussion.