A perfectly preserved note, never mishandled by the issuing authority, a bank teller, the public or a collector. Paper is clean and firm, without discoloration. Corners are sharp and square, without any evidence of rounding. An uncirculated note will have its original, natural sheen.
Some note issues are most often available with slight evidence of very light counting folds that do not "break" the paper. Also French-printed notes usually have a slight ripple in the paper. Many collectors and dealers refer to such notes as aUNC.