According to the What Is a Call Option and How to Use It With Example - Investopedia, a call option is a contract that gives the buyer the right, but not the obligation, to buy an underlying stock at a specified price (the strike price) within a specified time period (the expiration date). The seller of a call option is obligated to sell the stock if the buyer exercises the option. Pierre buys a call option on a stock, which means he has the right to buy the stock if he exercises the option. He can also choose not to exercise the option or sell it before expiration.