A theory, especially in ethics or aesthetics, that conceptions of truth and moral values are not absolute but are relative to the persons or groups holding them.
So the facts can only be understood if your in their context?
That reminds me, there's a nice quote I found against objectivity (somewhere along these lines) - "history is not a science as it cannot replicate the same events under the same circumstances".
It also depends on how meticulous you want to be in your definition of truth. Some historians are more *perfectionist* than others.
Ultimately, it cannot be defined. (that's relativism)