The short answer is it expires worthless. The long answer is it has no value. A call option is the right to buy a stock at a specific price (called strike price) on or before the maturity date. If the stock is less than the strike on the maturity date, no one would exercise it.
If you don't sell your options before expiration, there will be an automatic exercise if the option is IN THE MONEY. If the option is OUT OF THE MONEY, the option will be worthless, so you wouldn't exercise them in any event.