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."