My definition of camping is entirely reliant on whether you know someone is coming or not. The most simple example is: if you see someone coming and you wait behind a doorframe for him/her to run past, that's not camping, but if you wait behind the doorframe with the expectation that someone will run past eventually, that's camping. One is a tactic in response to a fluid situation: thinking on your feet. The other is undeniably still a strategy, but far less honorable and glorious.
With snipers, it's a similar situation: if you're not moving from cover to cover, looking for people to pick off, or at least in response to shifting spawns, you're camping. It can get a bit iffy in situations where people just keep on running through the same part of the map that you have overwatch on, since you know that people will go that way, but you're still sitting and waiting rather than actively hunting. In situations like that, I think it's a fairly honorable tactic, since it requires planning and skill, and it'd be almost silly to do anything else; it's the strategy that makes the most sense in the given situation.
With snipers, it's a similar situation: if you're not moving from cover to cover, looking for people to pick off, or at least in response to shifting spawns, you're camping. It can get a bit iffy in situations where people just keep on running through the same part of the map that you have overwatch on, since you know that people will go that way, but you're still sitting and waiting rather than actively hunting. In situations like that, I think it's a fairly honorable tactic, since it requires planning and skill, and it'd be almost silly to do anything else; it's the strategy that makes the most sense in the given situation.