A stock market index option is a type of option, a financial derivative, that is based on stock indices like the S&P 500 or the Dow Jones Industrial Average. They give an investor the right to buy or sell the value of the underlying stock index for a defined time period. Because index options are based on a large basket of stocks, they allow investors to gain exposure to the market as a whole and take advantage of diversification. Index options may be tied to the price of either "broad-based indexes" like the S&P 500 or the Russell 3000 or to "narrow-based indexes", which are limited to a particular industry. The global market for exchange-traded stock market index options was notionally valued by the Bank for International Settlements (BIS) at $368,900 million in 2005.