I gathered that it's your experience with a specific type of ring. Meaning, you get experience with a ring, you get better with that ring. If you sell the ring, the person you sell it to is back to square one, but you could use a ring of the same type just as well.
Edit: after a second look, it says you get better with "each individual" ring, meaning if you sell it, you and the person you sell it to are both back to the baseline.