I suspect truth could take long enough to unravel all by itself if you first ask the audience what they think it means, but on the other hand I think that what evidence is is a major issue on which most people are tremendously confused, and if you clarify that, a sense of what truth is will probably accompany it.

Important points to cover:

Conservation of evidence; people intuitively tend to raise their confidence, or at least not lower it, in the face of any evidence consistent with their beliefs.

Absence of evidence is evidence of absence; addresses such a common mistake that its negation is a popular saying.

Positive bias; one of the most pervasive biases preventing people from usefully testing their beliefs.

With just an hour, I think I'd focus on evidence and map vs. territory, or maybe even entirely on evidence.