HEeh, so after much forum perusal and searching for various phrasings of the terms hitbox and iframe I can't narrow down precisely enough what each of these terms mean. So far as I have determined it is as follows.
Hitbox - One or more areas on a monster that you can hit for damage period. Not necessarily the same as a weak point. But that a weak point would also be a hitbox.
iFrame - This is the more elusive for me. Best I've come up with is it has to do with how many attacks you can get in a fixed timeframe? Based on various daftness in PA (Photon Art) usage etc.
Any clarification/expansion of these would be much appreciated. Certainly by others whom don't want or aren't ready to admit their gaming knowledge deficiencies. I say that generically vs saying PSO2 NA as Hitboxes and iFrames are probably universal across most/all games. Something the game devs have to build and put into games.