A Beijing coin is a crudely phrased crossword puzzle clue in which the word "yuan" is the intended answer. A yuan is a unit of currency in China. The first Chinese-produced dollar coins were minted in 1890, and as of 2014, there are several denominations of yuan coins.
The official name for Chinese currency is actually not yuan but renminbi. This is translated into English as "people's currency." The renminbi is not a unit of currency. Rather, it is what the People's Republic of China calls all currency it mints or prints. Yuan are the standard unit of currency and come in coins and bank notes, whereas fen are smaller units analogous to American cents. The jiao is an intermediate unit worth 10 fen, or one-tenth of a yuan.