Arbitrage is a trading strategy that profits from a price difference for the same asset, or closely related assets, across different markets. You buy where the price is lower and sell where it is higher.
Arbitrage can appear in stocks, forex, commodities, bonds, futures, options, cryptocurrencies, and ETFs. Price gaps open because of market inefficiency, timing delays, liquidity gaps, differences between exchanges, or differences between pricing models.
Arbitrage opportunities are often small and close quickly as traders act on them. Before treating a price gap as real arbitrage, you account for transaction costs, execution speed, liquidity, slippage, and settlement risk, because any of these can wipe out the difference.
Gold trades at USD 2,350 on one exchange and USD 2,355 on another. You buy at USD 2,350 and sell at USD 2,355.
The gap before costs is:
2,355 - 2,350 = USD 5 a unit
It is real arbitrage only if you can complete both trades quickly and your costs stay below USD 5.