Within the context of put and call options based on an index, the strike price
is the price of the option that determines its value (or lack of value) at
settlement. If a put option's strike price is above the index's
settlement value, it is "in the money"—in other words, has value. The
opposite is true of call options—that is, if a call option's strike price
is below the index's settlement value, it is "in the money." When
the strike price and the index's settlement value are the same, this is
known as "at the money."