If the stock is NOT owned, they are uncovered calls and there is a substantial risk involved. The writer may be called upon to deliver stock at the exercise price regardless of how high the stock may have already appreciated to. But there aren't that many stocks that exceed the strike price PLUS the premium so that the owner at least breaks even. Owners of options do not have to hold them to maturity. They may sell them to others at any time.
Most people are familiar with options on stocks.
The seller hopes the stock will go up- or at least no place. The owner hopes that the stock will go down. In such case, the owner of the option has to right to force the seller to buy stock at the strike price.