Call option is an option contract that gives the holder the right to buy a certain quantity (usually 100 shares) of an underlying security from the writer of the option, at a specified price up to a specified date. The exchange of the stock is optional and the owner of the call option decides whether it takes place.

The agreed upon price of the exchange is called the strike price. The date on which the agreement expires is the expiry date of the call option. The amount of money required to purchase this call option is called the premium. If the exchange takes place, then one is said to have exercised the call option.

Call option premiums are always quoted per stock, but sold in lots of 100 shares minimum. Call options are always an agreement about being able to purchase the stock at the agreed upon price. Call options come in both European style and American style.