Tactical can mean a lot of things in the knife biz, but in the military sense, 'going tactical' means subduing all items that might give your presence away to the enemy. So that means bright, shiny objects, anything that might make a noise, etc. The classic example is taping dogtags together, or putting them in a plastic sleeve.
However, in the knife world its a whole other kettle of fish (or can of worms, depending on your degree of cynicism).
Basically, I see a 'tactical' knife as one that it is geared towards the dark arts, form following function, usually with a subdued finish, but not always, and lacking in any fancy add-ons or embellishments. Although this too is becoming less and less typical.
A classic example would be the Crawford Kasper, very much a tactical knife, but one that is also available with some very non-tactical embellishments...
But then that's why they call it a 'custom' knife I guess....
