Mint - A perfect card.
Mint/Near Mint - An unplayed, fresh out of the pack card.
Near Mint - A card that may have some minor wear from play (in sleeve) and/or manipulation or storage.
Lightly Played - A card that look like it was played without a sleeve. Minor whitening on the edges.
Moderately Played - Considerably played card. Whitening on the edges. May have some surface scratches.
Heavily Played - Major whitening on the edges and on the back, and/or surface scratches.