What does PSA 10 mean?

PSA 10 is PSA's top grade, Gem Mint. PSA describes it as "a virtually perfect card": four perfectly sharp corners, sharp focus, full original gloss and no staining. The image must be centered within about 55/45 on the front and 75/25 on the back. A slight printing imperfection may be allowed if it doesn't hurt eye appeal.

PSA can also return cards with no numeric grade, for example N1 (evidence of trimming) or N4 (questionable authenticity). See grading scales explained and PSA grading cost.