A call (or call option) is a contract that gives the holder the right to buy a stated number of units of the “underlying” asset at a given price (which is called the exercise price or strike prile, here we denote the price by Ｘ) from the counterparty (called the writer of the option).In the case of a European option,this right can be exercised on a given maturity date T,while for an American option it can be exercised at any time until the terminal date T. Depending on the underlying asset on which the option is written, a call can be an option on a stock,a stock market index, a currency, a commodity, a bond, or an interest rate,or even a futures contract or a swap (“swaption”). Currency option is popular. A call option allows you to obtain only the “nice” part of a forward purchase. Rather than paying Ｘ for the foreign currency (as in a forward purchase),you pay no more than Ｘ, and possibly less than Ｘ