A call gives investors the option, but not the obligation, to purchase a stock at a designated price by a specific time frame. Essentially, the buyer of the call has the option to purchase the security up until the expiration date. The seller of the call is also known as the writer. The writer must sell the security at the strike price until the expiration date.
Conversely, if an investor purchases a put option, they have the right to sell a stock at a specific price up until an expiration date. The investor who bought the put option has the right to sell the stock to the writer for their agreed-upon price until the time frame ends. However, the investor is not obligated to do so.