A state of mental and emotional honesty. When all pretense, prejudice, expectations, bravado, etc. are removed, and all that is left is the bare mind. Pure thought (not necessarily pure as in good) is more readily accomplished when one is psychologically nude. Note that psychological nudity has nothing to do with the amount of clothing one is (or is not) wearing; it is a mental state.
After half an hour of chipping away at my preconceived ideas, I could finally see what she was talking about. Fully clothed, I experienced psychological nudity.