Arbitrage

Arbitrage is the practice of buying an instrument in one venue and simultaneously selling it in another where it is priced higher, locking in the difference without directional risk. In currency markets the classic form is triangular arbitrage, where three pairs are momentarily inconsistent with one another.

In practice these opportunities are measured in fractions of a pip and last milliseconds, and they are harvested by co-located automated systems. For a retail trader, an apparent arbitrage on a retail platform is almost always a stale quote, a wide spread, or a cost you have not counted yet.