flat piece of metal issued by the government as money
PCGS uses the definition:
Metal formed into a disk of standardized weight and stamped with a standard design to enable it to circulate as money authorized by a government body.
The key points to the definition of a coin are:
- A hard (non flexible)
- government issued or approved item
- for use as general currency (not limited use such as a bus token)
- in a country, region, or area.
Currency issued by local governments are usually considered tokens (such as German notgeld) rather than coins, unless granted a mint right.