An Index Option is a financial derivative that gives the holder the right (but not the obligation) to buy or sell the value of an underlying index, such as the S&P 500 index, at the stated exercise price. This makes them useful for hedging against losses in a portfolio of stocks.Index options are typically American style, meaning they can be exercised at any time up to and including expiration day. European style options can only be exercised on expiration day. The value of an index option is based on changes in the underlying index it tracks.