What does FR stand for on a coin?

Answer 1

If it's part of the denomination, e.g. "10 FR", it means the coin comes from a country that uses (or once used) the franc as its primary currency unit.

Until the euro began in 2002, France and Belgium were the main European countries that used francs. They were different currencies but shared the same name, just like the US, Canada, and Australia all have currencies called dollars but they're not interchangeable.

Switzerland's currency is also called the franc, but it isn't part of the EU and never adopted the euro.