Industry standards for grading conditions of coins:
PF or PR: Proof. A specially made coin distinguished by sharpness of detail and usually with a brilliant, mirror-like surface. Proof refers to the method of manufacture and is not a grade. The term implies superior condition unless otherwise noted.
MS: Mint State. The terms Mint State (MS) and Uncirculated (UNC) are interchangeable and refer to coins showing no trace of wear. Such coins may vary slightly due to minor surface imperfections.
UNC or BU: Uncirculated or Brilliant Uncirculated. Coins showing no trace of wear. Such coins may vary slightly due to minor surface imperfections.
AU: About Uncirculated. Traces of light wear on many of the high points. At least half of the mint luster is still present.
EF: Extremely Fine. Light wear on design throughout, but all features sharp and well defined. Traces of luster may show.
VF: Very Fine. Moderate wear on high points of design. All major details are clear.
F: Fine. Moderate to considerable even wear. Entire design is bold with overall pleasing appearance.
VG: Very Good. Well worn with main features clear and bold, although rather flat.
G: Good. Heavily worn with design visible but faint in areas. Many details are flat.
AG: About Good. Very heavily worn, with portions of lettering, date and legend worn smooth. The date may be barely readable.
Other abbreviations you may come across:
Full Bell Lines
DC or DCAM:
Deep Mirror Proof-like
Special Mint Set / Satin Finish
Tail Feathers (on Morgan Dollars containing 7 or 8 Tail Feathers)