The rouble is the main unit of money in Russia, and also in Belarus — though those are two different currencies that only share a name. You hear prices in roubles the way you hear prices in dollars or in Taiwan dollars. American English often spells the same word ruble; British spelling keeps the -ou-. Both spellings are correct, and they do not name two kinds of money. Learner books often use rouble. The English word came in through French.

盧布（俄羅斯與白俄羅斯的貨幣名；兩國的盧布並不是同一種錢）。