There's a long standing joke in gaming circles that when a player unwittingly mentions a (meta)game concept in what is supposedly in-character dialogue, the NPC stares back with a blank stare, going: "The what now?"
Magic item merchant: "Perhaps this fine sword for the lady?"
Player: "What bonus does it have?"
Magic item merchant: "Bonus? I do not understand."
Back in this post I suggested a D&D society in which character class really designated their social class. It's one of those things where I'm tempted to grab the implied setting by the horns and ride it through the gate to its ultimate consequence. But is class one of those concepts that doesn't have an analogue in the game?
It's not a problem with some classes, because if you say "I'm a fighter." the meaning is going to be more or less the same: you're a guy that fights. But if a NPC tells the party that in the tower lives a "sorcerer of formidable skill" is he simply communicating that there's a demon-dealing magic-meddling person in the tower, or is the he communicating strategically important game information, that yes, there is indeed a Sorcerer (as opposed to a Wizard). If you say "I'm a paladin", do the people in the tavern understand that you can heal them by touch? Can you say "I'm a thief" even if you haven't stolen anything yet?
I think the issue (not really an issue but whatever) becomes the most obvious when you want to reskin a class. Is an urban ranger still a ranger? Is a barbarian who is a bio-engineered shock troop of an advanced culture still barbarous? Can you still say "I'm a fighter." when you're actually an archer?
I think it's an interesting thing to figure out for your game.