You can find most popular coin collecting phrases in this coin glossary.
unc or unk or UN - abbreviation for uncirculated.
uncirculated or un-circulated - a new condition coin that does not have any sign of wear. Marks on the coin that may come from the manufacturing process do not keep a coin from being un-circulated. (Example, bag marks.) Even the slightest amount of wear or cleaning will keep a coin from grading uncirculated.
upsetting mill - machine used in coin production to raise the rim on both sides of a blank (planchet).