That's a good question. What is true is often a matter of agreement. It is true that 2+2=4, because every variable is clearly defined, so there can be no question of the outcome. There isn't a lot to do with context here. 2+2 will always be 4.
But if we look at a statement: "Jack was mean to Joe". The truth of that statement depends on the context. Was he mean to Joe?
Imagine we called a trial to get to the truth of it. That trial would be a negotiation, and the truth would be the outcome of the negotiation. During the negotiation the context in which the truth would be decided would be agreed upon.
I am sure others have things to add, or can express these ideas clearer.