Maybe it would be called a relative pin, as opposed to an absolute pin. Except in this case the relative pin wouldn't be against a queen or rook but a checkmating sqaure.
What is it called?

If you cannot make a legal move, then it's a stalemate. If it's just a situation where you can make a legal move, but doing so will eventually lose the game, then it's called Zugzwang (pronounced tsook-svahng).
Even your pronunciation example is hard to pronounce lol. Quite a word indeed.

I think relative pin is different concept here what hez saying is piece has important duty 2 prevent mate ....kind of overloaded

Zugzwang (pronounced tsook-svahng).
I'd say tsook-tswung would result into a more accurate pronounciation. ^^

I'm asking because I was in a game and my opponent's Queen was in a position where if he moved the Queen away from protecting a specific pawn, I would have mate in 2. This allowed me to use my other pieces to work on mate, but the opponent had to work without his Queen because of the mate threat. I just thought there would be a chess term for what happened to that Queen. It is not a pin, and not really trapped (I think that trapped means something else--but I guess the piece could be trapped?). I also don't think that zugzwang quite fits.

I'm asking because I was in a game and my opponent's Queen was in a position where if he moved the Queen away from protecting a specific pawn, I would have mate in 2. This allowed me to use my other pieces to work on mate, but the opponent had to work without his Queen because of the mate threat. I just thought there would be a chess term for what happened to that Queen. It is not a pin, and not really trapped (I think that trapped means something else--but I guess the piece could be trapped?). I also don't think that zugzwang quite fits.
FWIW I call that being tied to defense. More formally I guess you'd call it passive defense (if that's the piece's only job and it can't afford to stop). I don't think there's a chess specific term for it.

Well if its a tactic name you are looking for, the tactic involves getting the piece to move. This is removal of the guard.

I think this is removing the guard, overloading, and relative pinning all mixed into one glopping mess of amazing victory.

I have called it a pin to a mating square and others seem to do the same
http://www.chesstactics.org/index.php?Type=page&Action=none&From=4,3,5,1

I have called it a pin to a mating square and others seem to do the same
http://www.chesstactics.org/index.php?Type=page&Action=none&From=4,3,5,1
Well he said the piece wasnt actually pinned. A diagram would help.
There are several motifs that could apply.
Wikipedia calls this a "situational pin" (ignore the incorrect pawn colors):
Overloading (ignore the grammar error, I'm too lazy to fix it):
Removing the guard (or distraction):

The way I took his explanation though, it was more positional in nature. There were no extra threats or attacks yet, but because the queen was unavailable in future maneuvers he was able to create extra threats. So the concept leads to a situation of a relative pin or being overworked, but at that moment it's not the same thing.
I know what a pin is in chess, but I was wondering if there was a term for another situation. Say you are in a position where if a piece moves, your opponent will put you in checkmate. The piece is not actually pinned, but still cannot move (a move would be legal, but would lose the game). Is there a name for that?