Near Mint (NM)
Cards in Near Mint condition do not show any kind of defects. They should correspond to cards freshly opened from a booster pack. The border of a Near Mint card can have one or two white spots on the border of the card, but they have to be very small. When the card is inspected under bright light, the surface must generally appear clean. It can have a few minor spots or scratches, but only in a very minor extent. Generally a Near Mint card is in a condition that it wouldn't be recognizable when mixed in a pile of booster-fresh cards.
Cards in Excellent condition show visible but very minor wear. Excellent cards usually have a couple of white spots at the corners or around the border. The surface may have minor scratches that are visible upon closer inspection. The card can be slightly dirty or clouded. An Excellent card is usually indistinguishable from a Near Mint card when in a perfect size sleeve.
Cards in Good condition are typically those which show Excellent-grade damage in but in a larger extent. This grade represents an intermediate step between slight imperfections and visible significant damage. The cards may show multiple light scratches or dirt spots on their surface or are more heavily clouded.
Cards in Played condition show visible extensive damage. Examples include extensively worn edges or corners, significant scratches, significant dents, flaked surface or slight shuffle creasing. Although Played cards show noticeable wear, their tournament legality should never be in question. If you're asking yourself if you could play a certain card in a sanctioned tournament, you're most likely holding a card that is Heavily Played.
Heavily Played (HP)
Cards in Heavily Played condition show significant damage. Examples include bend cards, cards with major edge or corner wear, major whitening, inking, major shuffle creasing, cards that have been written on, cards with water damage and damage comparable to previous examples. You can usually tell a Heavily Played card just by touching it even through a card sleeve. Cards damaged this way aren't usually tournament legal anymore.
Cards we do not buy
Cards falling into this category are cards we do not buy at all. They are either too damaged, meaning even in a worse condition than Heavily Played, or they are in an acceptable condition but in a language we are not interested in. Signed or altered cards also fall into this category.