Oh my, someone took an intro bio course.

Yeah, they're both classified under the same heading of "You shouldn't be able to do that". That much wasn't being argued.

One is supported by in game mechanics, the other is an abuse of it.

For example, the melee glitch. Nothing fancy about it, it was simply animation cancelling. L3+R3. You shouldn't be able to melee that fast, but it didn't do anything unreal to it. TONS of "high level techniques" fall into this category. Reload cancelling, wavedashing, hell ANY type of animation cancelling falls under this. Headglitching is also an exploit, which many complain about as well. It's just abusing the location of the camera and hitbox placement. They aren't "breaking the game", they're just taking advantage of systems in place. Once uncovered, its up to the game devs to decide if they want it or not. A lot of them stay (Such as reload cancelling, being in literally every FPS ever now). As much as some might disagree, I'm fine with a majority of exploits. They're not hard to duplicate and use by even lower tier players and they're not breaking the game. Hell, most of them even get their own in game counters. Like the uplink trick in objectives being countered by carrying fluxes. Nobody even complains about that any more.

However, lets say that instead of L3+R3, he did some weird messing around with depots and weapons and somehow managed to get his gun to "shoot" melee's. Yeah, like he presses R1 and his bullets do melee damage and list in the killfeed as "melee". Now we're in glitch territory. Something here has gone horribly wrong. The LAV glitch is like this. Invisible driver? Unkillable LAV? That's a glitch. It's not supposed to do that and everyone damn well knows it. It's not some odd gimmick, its blatantly taking advantage of a coding issue (or something to that effect) to grant himself benefits that far exceed the normal power of the original.

That is the difference I was pointing out. Nothing else.