SW - Shrink Wrapped. Still in the original factory shrink wrap, with condition visible through shrink noted. For example, "SW (NM)" means shrink wrapped in near-mint condition.
N - New - Brand new. Just like it was on the shelf at your favorite store.
M - Mint - Perfect. Brand new.
NM - Near Mint - Like new with only the slightest wear, many times indistinguishable from a Mint item. Close to perfect, very collectible.
EX - Excellent - Lightly used, but almost like new. May show very small spine creases or slight corner wear. Absolutely no tears and no marks, a collectible condition.
VG - Very Good - Used, may have medium sized creases, scuff marks, very small stain, etc. Complete, very useable, no major or "eye catching" flaws.
F - Fair - Very well used, but complete and useable. May have flaws such as tears, pen marks or highlighting, large creases, stains, marks, a loose map, etc.
P - Poor - Extremely well used and has major flaws. Item is complete unless noted.