13. What is "Premium Coin"?

The premium coin is a commemorative coin, made of precious metal, and is sold by the government at a price above the surface denomination.
The first one issued in Japan was the memorial gold coin of the Winter Olympic Games in Nagano.

*Informal translation
For accuracy and nuances, see Japanese original.
The law concerning a unit of currency, issuance of coinage and so on (1982, law, No.42)
Article 10 The Japan Mint sells coins authorized by the finance minister stipulated below.
1 The commemorative coin whose material includes precious metal, and whose production cost exceeds its surface denomination.