Call option is the right to purchase stock at a strike price at any time before the predetermined deadline. After the deadline, the option is expires.
The advantage of a call option is the ability to control a large amount of shares with just a little bit of money. If the option never makes the call price though, you lose all of your money paid for the option. (such as a call option to buy WMT at 50 at $2 a option with a May deadline. Your cost is 2 dollars for every option you take. So if you take 10 options and WMT makes it to 55 in May u make $3 a option)