"Trip Guard" is a term that's been around since SF2 but its exact meaning isn't very clear, well-known, well-documented, and when the term is used, it's used kind of loosely as well. Don't quote me on any of this I'm about to say, I'm not super confident on how accurate the details are.
The idea is that trip guard in SF involved being in a jump and getting hit by a sweep as you land which was kind of peculiar because the sweeps in question had such low hitboxes that they shouldn't really be able to connect with someone in the air, but if they landed on the ground, they should have been able to block, yet got hit.
So what we're discussing here is the same idea, with air recovery as you land. I think the actual "trip guard" referred to having little or no landing recovery in a game (since games in the series differed with this, along with a ton of other things ofc), since a character would be guarded from being tripped after a jump (since most people just used sweeps for the knockdown and pushback)
Also IIRC I believe landing recovery can also be cancelled in some situations (def. not on whiff)? Since (to my memory, I play mostly F these days), if you connect a jump-in and then land and hit A (or B if you jumped in with C) you get a reverse beat message.
To find out if something is safejumpable or not, air recovery needs to be one frame faster than the startup of the reversal. This is because you would need at least one frame of the jump-in being meaty. Think of the air recovery as the startup for a block, but you're always starting it at least one frame after the reversal if you still want the meaty OS.