What is Truth?

We're reading Fides et Ratio in my History of Ideas class, and we got into a really interesting discussion about truth.  

My professor was saying that people have different capacities for truth, so the people who have higher capacities have a better understanding of the whole truth, and the people with lower capacities may have part of the truth, but they aren't as accurate in their view of truth.  After that mouthful of a concept, I had a lot of questions that I didn't know how to phrase.  So even though it sounds like I'm trying to argue like a relativist, here's how I started out the conversation with my professor: But truth is not relative, correct?