The standards our curators use to grade items, and what sellers must follow when writing item descriptions. If you're a buyer, this also helps you understand the condition terms used in each listing.
TCG cards (Pokémon and the like) are judged on two things: whether they have been graded by an official body (slabbed) or are still raw, and their physical condition.
Assessed by an official body (PSA, BGS, CGC) and sealed in a hard plastic case with a score from 1 to 10. The score is printed on the slab label and can be cross-checked in that body's database.
An ungraded card in near-perfect condition: sharp corners, no scratches, no whitening along the edges.
Light signs of handling: a little whitening at the corners, surface still glossy, no creases.
Clear signs of play: creases, rounded corners, surface scratches. Perfectly fine to sell, as long as it is described honestly.