True arbitrage is the risk-free profit from short-selling one over-priced instrument and simultaneously buying an under-priced instrument. The attributed mispricing of the securities in such a case reflects a market inefficiency, in which relevant information has not been included in the prices. The arbitrage trade is supposed to correct that mispricing through the information that motivates it. Most so-called arbitrage trades are not risk free because the validity of the information held by the "arbitrageur" (a person who engages in arbitrage) is subject to debate. Thus, much arbitrage activity constitutes a form of market debate about correct price levels. The term is mainly applied to trading in financial instruments, such as bonds, stocks, derivatives, and currencies.