Legal tender is anything recognized by law as a means to settle a public or private debt or meet a financial obligation, including tax payments, contracts, and legal fines or damages. The national currency is legal tender in practically every country.
For example, Hong Kong Dollar (HKD) is the legal tender of Hong Kong SAR. Chinese Yuan (CNY), or as known as Renminbi, is the legal tender of the People's Republic of China. British Pound (GBP) is the legal tender of the United Kingdom.