Coin grading has the longest-established vocabulary of any collecting category, and it rewards precision.
The scale
The standard numeric scale for coins runs 1 to 70, with descriptive bands beneath it — poor, fair, good, very good, fine, very fine, extremely fine, about uncirculated, uncirculated.
Confusingly, "good" is near the bottom. A coin described as good is heavily worn. This catches everybody once.
Uncirculated
Never used as money. No wear on the high points.
It is not the same as shiny, and it is not the same as attractive. A dull original uncirculated coin outranks a bright polished one by a wide margin.
The word that costs most
Cleaned. It must be declared. A cleaned coin is worth substantially less, the damage is permanent, and experienced buyers can see it — so concealing it does not work and turns a lower price into a dispute.
If you do not know whether a coin was cleaned before you got it, say exactly that.
Toning
Colour acquired over time. Natural toning is often desirable; artificial toning is not, and telling them apart is an experienced judgement rather than a rule.
Notes
Graded on their own scale, with crispness, folds, corners and any pinholes all counting. A single fold moves a note several grades.
Never press or flatten a note. Same principle as cleaning a coin.
Questions people ask
Why is "good" bad?
Historical accident. The scale predates the plain meaning.
Can a cleaned coin be restored?
No. The original surface is gone and nothing puts it back — which is why the word has to be declared rather than hoped past.
What about a coin in a holder?
The number on the label is that company's assessment. Check the label and the coin together.