A very basic example of this would be if you lived in a town that grew lots of apples. Due to the abundance of apples, the cost is 4 for a dollar. A few towns over doesn't grow as many apples, so the cost is 2 for a dollar. You decide to make money by purchasing them in your town and selling them for a better price at the other town. You have just engaged in arbitrage. Purchasing one asset from one market, in order to make a profit selling the same asset in another market.