Arbitrage

In economics and finance, arbitrage is the practice of taking benefit of a price differential between two or more markets: a mixture of similar deals is struck that take advantage of upon the imbalance, the profit being the difference between the market prices. When used by academics, an arbitrage is a transaction that involves no negative cash flow at any probabilistic or temporal state and a positive cash flow in at least one state; in simple terms, a risk-free profit. A person who engages in arbitrage is called an arbitrageur. The term is frequently applied to trading in financial instruments, such as bonds, stocks, derivatives, commodities and currencies.

If the market prices do not allow for profitable arbitrage, the prices are said to encompass an arbitrage equilibrium or arbitrage-free market. Arbitrage equilibrium is a precondition for a general economic equilibrium. The assumption that there is no arbitrage is used in quantitative finance to calculate a unique risk neutral price for derivatives.
Statistical arbitrage is an imbalance in predictable nominal values. A casino has a statistical arbitrage in almost every game of possibility that it offers - referred to as the house edge or house advantage or even the Vigorish.