Sniper is a person/training/use case, but the term “sniper rifle” (while sometimes misused) is still a useful and descriptive term. It distinguishes itself from “comp” guns in that most soldiers aren’t going to strap ridiculous extra weights onto their gun because they actually have to carry them. The scope will probably be overbuilt (unlike a benchrest scope). It will probably have a bipod, since it won’t be nestled into a lead sled. A certain range of calibers is implied. We can make reasonable assumptions about the adjustments and the reticle (probably not a duplex), Etc.
“3 gun” is an activity, but “3 gun AR” is a useful descriptive term. It tells us that longer barrels, flashy colors, muzzle breaks, and other things are allowed in the build, whereas most people wouldn’t use those features for a serious use AR. It also tells us that “upgrades” that give time advantages are acceptable even if they slightly harm reliability… there is no other category in which this is generally accepted as a reasonable trade off.
Home defense is an action, but “home defense AR” is still a descriptive term that tells us you’re building a close range gun, probably very simple, and probably equipped with a red dot and white light. We probably know not to advise bipods and high magnification scopes to a guy wanting a HD AR.
Concealed carry is an activity, but saying you’re looking for a concealed carry gun still helps us know that our favorite S and W 500 magnum with 12” barrel probably isn’t the best recommendation.
Recce: All the same concepts apply.
A Recce AR is built to be significantly more accurate/precise than most ARs. (This is the prime distinction between Recce and “do all” or “general purpose”)
It will need some type of magnified optic to do this. It also needs to be capable up close, so high magnification scopes are out unless accompanied by a red dot. This leads most to LPVOs or red dots with magnificatiers.
It will need a premium barrel (unless you get lucky with a unicorn production barrel). If it’s a free floated AR without an upgraded barrel, we’re talking about a general purpose AR, not a recce.
Etc, etc, etc.
I’ve seen the term “recce” bother a few people recently and it always makes me shake my head. Those people are ALL guilty of using at least some of the other terms.