Definition of an Index Option: An index option is the same as an equity or stock option, except the underlying asset is an index instead of a stock. Just like an equity call option, an index call option is the right to buy the underlying index. And just like an equity put option, an index put option is the right to sell the underlying index. At this point, you can exercise your call option and buy the stock at $40 per share instead of the $50 it is now worth - making your $200 original contract now worth $1,000 - which is an $800 profit and a 400% return. What are index call options? The buyer of an index call option has purchased the right, but not the obligation, to buy the value of the underlying index at the stated exercise price before the option expires. Once the option is purchased the buyer owns, and is then "long," the call contract.