noun
commemorative coin
A coin issued to mark a special event, anniversary, or person. Often collected or kept as a souvenir.
東京オリンピックの記念硬貨を買いました。
I bought a commemorative coin for the Tokyo Olympics.
記念切手 is a commemorative postage stamp, while 記念硬貨 is a commemorative coin.
Compound of 記念 (commemoration) and 硬貨 (coin).