I thought we agreed that, "truth" is a concept ( used in a social context) . . ." to create a focal point upon which to argue "what is and what is not" and that if we got rid of the term "truth" we wouldn't argue about the line in the sand, or even where the line in the sand is placed!
Truth isn't a concept. It's a value. Think of it as a switch for something else. There are various kinds of switches, but they all amount to either "on" or "off". What you said, something is "true" if we agree it is "true", is still such a swtich: "true" if we agree, "false" if we don't. Ultimately, that kind of idea of "truth" is correspondence, since our claim "this is true" has to correspond to the agreement previously made. Such things as important but banal social conventions ("Say excuse me when you bump into someone") and things like traffic rules (right-of-way, using a signal to change lanes, stop at a red light) -- there's no necessity behind them, they didn't have to be that way, yet they become "true" by virtue of being codified, either explicitly (laws) or implicitly (norms).