In my opinion, a knife is tactical when it's intent and purpose is other than hunting, art, or historical significance. This basically leaves combat, defense and offense weapons. Military use, camping and bushcraft knives as well as several styles of Everyday Carry's (EDC) all fall into this popular category. Make it look mean, square up the edges a little bit, add some grippy g10, carbon fiber or cord wrap and you are in the realm of "tactical".
I think of "task specific" when I think of the tactical knives I make. You may not like their purpose, but you will agree that in the proper hands they will perform as designed. Look at a Coye Ridgeback, a George or Curtiss folder, a Barker or any of a dozen other makers on this site and "tactical" explains itself. I truly appreciate and own all types of knives (about 250 pcs now) and the technical and mechanical beauty of a fine tactical equals the flowing lines and artistic beauty of a sweeping bowie or drop point hunter.
In firearms, it's the difference between fine shotguns and full blown spec'd out 1911's. I for one, want both.
Just my opininion, for what it's worth.
Respectfully submitted,
Steve