The seller of a call option may be obligated to fulfill the terms of the contract and sell the underlying stock at a specific price in exchange for the premium they have received. (us.etrade.com)
Likewise, the seller of call options is obligated to sell stock at a certain price by a certain date if the buyer chooses to exercise his right. (borntosell.com)
The owner of the call option literally has the right to «call» the stock from the seller of the call option at a specified price. (us.etrade.com)