The following grades and description are from the ANA's officia grading terminology and standards guide. There is specific information listed in The Official American Numismatic Association Grading Standards for U.S. Coins under the various coin types, for wear often occurs in different spots on different designs.
Uncirculated Coins:   
MS-70 - The perfect coin. Has very attractive sharp strike and original luster.  No contact marks are visible under magnification.  There are no noticeable hairlines, scuffs, or defects. Has exceptional eye appeal.
MS-69 - Has very attractive sharp strike and original luster, with no more than two small non-detracting contact marks or flaws.  No hairlines or scuff marks can be seen.  Has exceptional eye appeal.
MS-68 - Has attractive sharp strike and original luster, with no more than four light scattered contact marks or flaws.  No hairlines or scuff marks show. Has exceptional eye appeal.
MS-67 - Has original luster and normal strike.  May have three or four very small contact marks and one more noticeable but not detracting mark.  One or two small single hairlines or one or two minor scuff marks or flaws may be present.  Eye appeal is above average.
MS-66 - Has above average quality of surface and mint luster, with no more than three or four minor or noticeable contact marks.  A few light hairlines may show under magnification, or there may be one or two light scuff mark showing.  Eye appeal is above average.
MS-65 - Shows an attractive high quality of luster and strike.  May have a few small scattered contact marks, or two larger marks may be present.  One or two small patches of hairlines may show.  Noticeable light scuff marks may be seen on the high points of the design.  Overall quality is above average.
MS-64 - Has at least average luster and strike.  Several small contact marks in groups, as well as one or two moderately heavy marks may be present.  One or two small patches of hairlines may show.  Noticeable light scuff marks or defects might be seen within the design or in the field. Overall quality is attractive.
MS-63 - Mint luster may be slightly impaired.  Numerous small contact marks and few scattered heavy marks may be seen.  Small hairliens can be visible without magnification. Several scuff marks or defects may be present throughout the design or in the fields.  The quality is about average, but overall the coin is rather attractive.
MS-62 - An impaired or dull luster may be evident.  Clusters of small marks may be present throughout with a few large marks or nicks in focal areas.  Hairlines may be very noticeable. Large unattractive scuff marks might be seen on major features.  The strike, rim, and planchet quality may be noticeably below average. Overall eye appeal is below average.
MS-61 - Mint luster may be diminished or noticeably impaired, and the surface may have clusters of large and small contact marks throughout.  Hairlines could be very noticeable.  Scuff marks may show as unattractive patches on large areas or major features.  Small rim nicks and striking or planchet defects may show, and the quality may be noticeably poor.  Eye appeal is somewhat unattractive.
 MS-60 - Unattractive, dull, or washed-out mint luster may be evident.  There may be many large detracting contact marks, or damage spots, but no trace of circulation wear.  There could be a heavy concentration of hairlines or unattractive large areas of scuff marks.  Rim nicks may be present, and eye appeal is very poor.
Circulated Coins:
AU-58 (Almost Uncirculated -58) - The barest trace of wear may be seen on one or more of the high points of the design.  No major detracting contact marks will be present and the coin will have attractive eye appeal and nearly full luster, often with the appearance of a higher grade.
AU-55 (Almost Uncirculated-55) - Only small patches of wear are visible on the highest points of the design.  Eye appeal and surface are above average.
AU-53 (Almost Uncirculated-53) - Noticeable spots of wear on several high points.  Very few contact marks or blemishes and generally good eye appeal.  Luster is diminished.
AU-50  (Almost Uncirculated-50)  - Shows traces of wear on many of the highest parts of the design.  On many of these coins, some of the original mint luster is still present.  May have a few noticeable contact marks or flaws.
XF-45  (Extra Fine - 45) - Has light overall wear on the coin's highest points.  All design details are very sharp.  Mint luster is usually seen only in protected areas of the coin's surface.
XF-40  (Extra Fine - 40) - Has only slight wear but more extensive than a XF-45, still with excellent overall sharpness.  Traces of mint luster may still show.  All design elements show clearly.
VF-35  (Very Fine - 35) - Surfaces show light overall wear with minor blemishes. May have one or two small rim nicks.  All details show clearly.
VF-30 (Very Fine - 30)  - Light even wear shows on surface; design details on the highest points begin to soften, but all lettering and major features are bold.
VF-25 (Very Fine - 25) - Entire surface shows light signs of wear and softening of design elements.  Major features are strong and clear.  Some of the minor details blend into the design.
VF -20 (Very Fine - 20) - Moderate noticeable wear on the higher parts of the design.  Minor details are beginning to flatten.  Surfaces are attractive and free of serious blemishes, erosion, nicks, or scratches.
F-15 (Fine - 15) - Shows moderate even wear through the surface.  Entire design is bold and clear with traces of flattening.
F-12 (Fine - 12) - Moderate to considerable even wear.  Entire design is in bold.  All lettering is visible, but may only show parts of the letters.
VG-10 (Very Good - 10) - Even wear throughout the entire coin.  Parts of the rim may be flat but still discernable.
VG-8  (Very Good - 8)- Well worn. Major design elements are visible, but with faintness in areas.  
G-6 (Good - 6) - Heavily worn, but will clean attractive surfaces and no major blemishes.  May have a few rim nicks and scratches.  Rim is very weak but basically complete.
G-4 (Good - 4) - Heavily worn.  Major design elements are visible, but with faintness in areas.  Rims may be incomplete in spots.
AG-3 (About Good - 3)- Very heavily worn, with portions of the lettering, date, and legends worn smooth.  The date is barely readable.  The date is barely readable.
Fair-2 - Most of the design details are worn completely smooth.  May have serious nicks, dents, and defects.
Poor-1 - Only the basic coin type is identifiable. Date and mintmark must be strong enough to be readable.  Entire surface is worn and may be disfigured by numerous blemishes. 
Please note: Coins that are bent, corroded, scratched, holed, nicked, stained or mutilated are worth less than undamaged coins.  Coins that have been cleaned, whizzed, buffed or polished to simulate Uncirculated luster are worth considerably less than un-cleaned coins.