What is Arbitrage?

Buying the same asset in a cheap market and simultaneously selling it in an expensive market in order to profit from the difference in its prices in different markets. There is arbitrage in currencies, securities, commodities and interest rates. When many participants simultaneously buy in the cheap market and sell in the expensive one, prices converge, so such a difference usually does not last long. In true arbitrage there is almost no risk; transaction costs and time differences can eat up the profit.

Source: Britannica: arbitrage (finance)