Most dictionaries give definitions like “a piece of information presented as having objective reality” or “a thing that is indisputably the case.”
I’ve got a different, much more functional definition for you that I think makes more sense: A fact is something that everybody present agrees on, or at the very least, a large majority. Otherwise, you can’t functionally call it a fact.
When there is a disagreement, if you continue to claim something as fact and the other person does not agree with you, you will get nowhere. Much of the time, resolving a disagreement simply requires that you clarify what people’s assumptions are.
A good tool to remember the next time you get tangled up in one of those stubborn arguments. 🙂