Card Condition Guide courtesy of Blackborder.com. We are posting this because numerous people said this is the guide they use.
Mint
This card has no defects whatsoever. It is in perfect condition.
Near Mint
This card is indistinguishable from a mint card unless you look extremely carefully. It has only very minor wear, which is often undetectable except by the experienced. This condition is so close to mint that many sites, including Blackborder, group the two conditions together and treat them the same.
Excellent
Sometimes called "Very Fine". This card has wear that can be seen by the untrained eye, but only a very small amount. Slight edge wear and/or minor scratches may be present, but damage is only really noticeable on close inspection.
Fine
This card has obviously been played. Sometimes also called "Played". It will have more minor defects than an excellent card, but no major defects. There may be quite a lot of wear on the edges and/or many scratch marks.
Good
This card has been heavily played. It may have a large amount of edge wear, permanent black marks and a lot of scratches, or it may be an otherwise M, NM or EX card with one or two major defects such as water damage, a slight tear, or a noticeable crease.
Poor
This category covers all cards which are more heavily damaged than a Good condition card. Poor cards are not just visibly played and worn, they are visibly damaged. A card in this condition is usually worthless unless it is particularly rare or sought after such as Power Nine cards and other Vintage and Legacy "high value" cards. These higher value cards will command a higher percentage sale value as well.
WUBRGPauper Battle BoxWUBRG ... and why I am not a fan of Wayne Reynolds' Illustrations.