A rough guide to my grading -

Near Mint - A card that is very close to its original state when taken out of a brand new pack. Near mint cards can have very minor flaws - typically, minimal whitening, minor chipping and light surface scratches. This is a top quality option and price will reflect this. 

Excellent - Usually a bit more wear on the edges / corners than a near mint card, but will still have most of the original edge. May also have surface scratches, very small amounts of edge chipping / scuffing and occasionally minor black dots. There should be no creases on an excellent card. A good option for anyone who wants a great condition card at a lower cost to that of near mint. 

Light Play - Fairly worn around the edges and corners, might have most or sometimes all of the back edges and corners whitened. May have scratching, edge and corner chipping / scuffing, moderate black dots, surface marks, indents, minor / small / light creases. This is good option for completing whole sets for a lower cost and retaining some quality.

Moderate Play - Cards will likely have any of the following - whitening, heavy wear on the edges and corners, moderate - heavy black dots, scratching, edge and corner chipping / scuffing, surface marks, indents, moderate creasing, discolouration / fading. In general these cards have been used many times and have seen better days, but they are still a good option for anyone who isn't too bothered about condition or that is wanting to fill in the empty spaces of sets and keep costs low.

Heavy Play - This is it people, the worst of the worst. Cards are in poor condition and will usually display flaws all over. The sky is the limit when it comes to heavy play. Potentially having any or all of the following, heavy wear on the edges and corners, whitening, black dots, scratching, edge and corner chipping / scuffing, surface marks, indents, creases, discolouration / fading, pen, ink, staining, folds, paper loss, parting of card layers, etc. What these cards lack in condition quality they make up for in character, they are a true testament to the history and nature of trading cards. This is the best option for someone who isn't bothered by condition and just wants a copy of the card for a much lower price.