I always understood it as Personal Survival Kit. Most peoples PSK's wouldnt fit in a BDU pocket.
I think that depends on your background.
I've seen "Kit, Survival, Individual" and "Kit, Survival, Personal" as descriptions for NSNed items, along with to "Kit, Survival, Aircrew" (more than one person?). From that perspective, PSK is a personal kit.
To others, the PSK is the last resort of the last resort, the tiny kit you put into the pocket you sewed onto your long johns, on the odd chance that you could lose everything else, probably including the contents of your pockets, when the boat sinks, airplane impersonates a rock, or a bear is snacking on the rest of your gear when you get back from taking a leak.
I fit into the later category myself, but I also layer my kit. Until I'm down just my PSK and maybe a pocket knife, it isn't really survival time. If I have my vest (ditch kit), I might have an emergency, but it isn't really a survival situation in most cases. With my pack, I can't have a non-medical emergency unless something is trying to eat me- I might have a surprise camping trip, but that is about it.