A contract that gives its owner the right to buy (call option) or sell (put option) a stock index at a fixed value until a specified date. Options are traded on the S&P 500, the S&P 100, the NYSE Composite Index, and the Major Market Index, along with specialized indexes. These options work exactly like regular stock options except that an index rather than a particular stock is the underlying asset. As with stock index futures, delivery must be in cash because it is not possible to deliver an index. See also Section 1256 contracts.