Bid and offer

Exchange rates in practice are quoted as two-way rates. Thus a dollar/mark quotation will read something like 1.5000/10. The bank or company which quotes this rate understands that it buys marks (selling dollars) at 1.5010 and sells marks (buying dollars at 1.5000). In other words it buys cheaper and sells dearer a given currency in exchange for the other one. Of course, the opposite is true for the person that asks for a quotation. The difference between the purchase and the sale rates is called "spread". Such spreads vary in size according to market volatility.