In Alaska, "snag" means to hook a fish elsewhere than in its mouth (see "Prohibited Acts").
The legal definition of snagging most assuredly varies from state to state. Perhaps it's time the rule-makers reconsider the definition within the context of the modern-day fishery. Especially on Alaska's most popular river fishing for Alaska's favorite meat-market quarry, the sockeye.
Since this is all about the recreational pursuit of fish with rod and reel (angling), it would be beneficial first off to consider the definition of what constitutes "snagging" from the perspective of angling ethics.
If the fish is chasing the gear in willful pursuit, it's legitimate angling from the perspective of "fair chase". This is the most fundamental element of our chosen sport... the fish is enticed to willfully strike the angler's offering. From an ethical standpoint, snagging is simply hooking a fish that does not willfully bite the angler's chosen presentation. If the gear is chasing the fish, then it's snagging, pure and simple.
From the standpoint of willful take, it matters not which way the poky piece of metal finds its way into the fish's mouth.... whether inside-out or outside-in is completely irrelevant as long as the hookup is the result of willful take on the part of the fish. The fish willfully bit and was hooked in its willful pursuit of the gear. Who cares which way the hook goes in!
In WA, willful take is the key element in defining whether or not the fish is legal to keep. As long as it was hooked in active pursuit of the gear, a fish can be hooked anywhere on the head and it's legal to keep within the constraints of the current season/bag limit for that species.
It gets a bit stickier in AK when one considers a meat-market species like sockeye where flossing has clearly become the entrenched method of recreational harvest. It's how the overwhelming majority of sockeye are LEGALLY harvested with hook/line.
Flossing IS most assuredly snagging from an ethical perspective.... the gear is clearly chasing an unwilling fish that wants no part of the "presentation". But willful pursuit is nowhere to be found in AK's legal definition of snagging. Alaska's version of snagging is defined simply as hooking the fish somewhere other than the mouth. Snagged (gear chasing the fish) in the mouth is perfectly legal in the Great Land. Snagged anywhere else is NOT.
Flossing is universally accepted by the users and the managers alike. It allows a meaningful, orderly recreational fishery to efficiently harvest sockeye by the hundreds of thousands. The most controversial aspect of flossing (as evidenced by at least 3 concurrent threads discussing the subject) is hook placement. It all boils down to this.... is one form of legitimized snagging (inside out) really any more "legitimate" than another (outside-in)? That seems to be a real hangup for a lot of folks... the ones insisting that their version of snagging holds the moral high ground because the sharp poky piece of metal first penetrates from within the mouth.
Indeed there is considerable ambiguity in the phrase "in the mouth" and how it is enforced. Some overzealous LEO's have been quoted as stating inside out is the only legal penetration, but that is NOT literally specified in the regs... it's simply individual interpretation.