I've primarily encountered it being used as jargon. Personally I'm not against jargon necessarily, but that concept is one of my least favorite aspects of Marxist readings of Capital: his critique of exploitation.
In that context exploitation is basically a description of how not all of the monetary benefits of a worker's labor-power are ever returned to her via wages. The reason being that the price of her labor-power is determined by the cost of her survival, whereas the price of the goods she produces is determined by other factors. Obviously there's a ton of problems with that line of critique, number one being that if you were to adopt it in isolation from the rest of Marx's critique, which unfortunately is what is often done, then it seems like you would assume that it's worthwhile for the worker to be engaged in that production in the first place and that the only objection you need to raise is one having to do with fairness.
Since I don't want people to think I mean anything like that, I avoid using the term even in a colloquial way. (another reason not to use this term, for me, is that in its colloquial sense "exploitation" has a very moral ring, and people who use it are generally doing an even worse type of analysis than the one attributed to Marx...)
(However, I want to add that the critique of exploitation, properly understood, is really just one part of his critique of alienation. That critique ultimately is not predicated on fairness or morality at all. I find it much more worthwhile and much more complicated to dismiss).