Error – Usually a mis-made coin not intended for circulation, but can also refer to an engraving or die-cutting error not discovered until the coins are released to circulation. This may result is two or more varieties of the coin in the same year.
Exonumia – The study of coin-like objects such as token coins and medals, and other items used in place of legal currency or for commemoration.
Fineness – Purity of precious metal content expressed in terms of one thousand parts. 90% is expressed as .900 fine.
