Why Grade Coins?
Most collectors prefer coins in the best condition possible, for obvious reasons. A coin in mint condition will retain more of the fine detail of the original engraving, ancient coins are easier to read in better states of preservation, and there is generally more pleasure in owning a coin in almost perfect original condition than a worn specimen.
There are less "old" coins in mint condition than in worn condition.

Value Depends on Condition
These two factors combine, low supply and high demand, so that prices for perfect condition coins are higher than for similar worn coins. In many cases, coins worth hundreds of pounds in mint state might be almost worthless in worn condition.

Standard Terminology
For many years dealers and collectors have used an almost universal scheme for describing coin grades. There are some differences between different national grading systems, but these are mainly boil down to differences in the descriptions used, rather than any real underlying differences.

Other Factors
Weak striking sometimes needs to be taken into consideration. A weakly struck coin in mint condition might show less detail than a better struck coin in only EF condition.
With hand hammered coins, such as ancient coins, many were struck off-centre, and well centred coins are usually preferable to off centred ones. This relates more strictly to the original state of the coin, rather than its preservation, but remains an important part of the description of the overall state of the coin, and therefore affects its desirability.

Abbreviations
Most dealers and collectors use "shorthand" abbreviations for grades, both in speech and in print.
The table which follows, or similar, can be found in most decent coin catalogues.

Abbr.	Grade	Description
FDC	Fleur-de-Coin	Absolutely flawless, without any wear scratches or fingerprints.
Unc.	Uncirculated	In new condition as issued by the mint, but not necessarily perfect
B.U.	Brilliant Uncirculated	As uncirculated, and bright. Sometimes used as type description meaning "non=proof" or superior normal.
EF	Extremely Fine	Slight surface marks or slight wear visible on close inspection.
VF	Very Fine	Some wear on the raised surfaces, but still retaining much detail.
F	Fine	Considerable wear on the raised surfaces, all main features still sharp.
fr	Fair	Very worn, but all inscriptions and main features distinguishable.
poor	Poor or Worn	Very worn, some features or lettering worn away.

Proof
Proof is not a grade, but a term for a specially struck coin, often with matt design against mirror finish background, produced originally as pre-production samples, now often marketed for collectors.

Good
Although "good" is used in American grading meaning a coin which is not good, we use it in connection with the above terms, so that, for example, "good Fine" means "better than Fine".

Almost or About
We use "almost" or "about" to mean "not quite as good as", so for example "almost Fine" means "not quite Fine".

Art Not Science
It is important to realise or remember that grading is not a precise science. Opinions about grade will vary between individuals. Even expert dealers will grade a coin differently on different days. Grading is an attempt to achieve a reasonably standard set of descriptions, mainly to facilitate trade between collectors and dealers especially when dealing by mail order or telephone.

Dealer's Descriptions
Most professional dealers try to grade consistently. When selling by mail order, most dealers allow a reasonable approval or return period, ours is 7 days. We try to grade accurately and consistently, partly from pride, but also from the very practical viewpoint that we would prefer customers not to return coins, it creates much less work for us if our customers are pleased with the coins they receive, and wish to keep them.

Grading, Independent Coin Grading Services
A slighlty imperfeect answer to a perennial problem.