What is Call Option?

Legal Definition
A call option, often simply labeled a "call", is a financial contract between two parties, the buyer and the seller of this type of option. The buyer of the call option has the right, but not the obligation, to buy an agreed quantity of a particular commodity or financial instrument (the underlying) from the seller of the option at a certain time (the expiration date) for a certain price (the strike price). The seller (or "writer") is obligated to sell the commodity or financial instrument to the buyer if the buyer so decides. The buyer pays a fee (called a premium) for this right.

When you buy a call option, you are buying the right to buy a stock at the strike price, regardless of the stock price in the future before the expiration date. Conversely, you can short or "write" the call option, giving the buyer the right to buy that stock from you anytime before the option expires. To compensate you for that risk taken, the buyer pays you a premium, also known as the price of the call. The seller of the call is said to have shorted the call option, and keeps the premium (the amount the buyer pays to buy the option) whether or not the buyer ever exercises the option.

For example, if a stock trades at $50 right now and you buy its call option with a $50 strike price, you have the right to purchase that stock for $50 regardless of the current stock price as long as it has not expired. Even if the stock rises to $100, you still have the right to buy that stock for $50 as long as the call option has not expired. Since the payoff of purchased call options increases as the stock price rises, buying call options is considered bullish. When the price of the underlying instrument surpasses the strike price, the option is said to be "in the money". On the other hand, If the stock falls to below $50, the buyer will never exercise the option, since he would have to pay $50 per share when he can buy the same stock for less. If this occurs, the option expires worthless and the option seller keeps the premium as profit. Since the payoff for sold (or written) call options increases as the stock price falls, selling call options is considered bearish.

All call options have the following three characteristics:

  1. Strike price: this is the price at which you can buy the stock (if you have bought a call option) or the price at which you must sell your stock (if you have sold a call option).
  2. Expiry date: this is the date on which the option expires, or becomes worthless, if the buyer doesn't exercise it.
  3. Premium: this is the price you pay when you buy an option and the price you receive when you sell an option.

The initial transaction in this context (buying/selling a call option) is not the supplying of a physical or financial asset (the underlying instrument). Rather it is the granting of the right to buy the underlying asset, in exchange for a fee — the option price or premium.

Exact specifications may differ depending on option style. A European call option allows the holder to exercise the option (i.e., to buy) only on the option expiration date. An American call option allows exercise at any time during the life of the option.

Call options can be purchased on many financial instruments other than stock in a corporation. Options can be purchased on futures or interest rates, for example (see interest rate cap), and on commodities like gold or crude oil. A tradeable call option should not be confused with either Incentive stock options or with a warrant. An incentive stock option, the option to buy stock in a particular company, is a right granted by a corporation to a particular person (typically executives) to purchase treasury stock. When an incentive stock option is exercised, new shares are issued. Incentive options are not traded on the open market. In contrast, when a call option is exercised, the underlying asset is transferred from one owner to another.
-- Wikipedia
Legal Definition
A DERIVATIVE contract that gives the buyer the right, but not the obligation, to purchase an UNDERLYING ASSET from the seller at a set STRIKE PRICE at, or before, expiry. In exchange, the buyer pays the seller a PREMIUM. Calls, which can be written on a broad range of financial and commodity references, are available as EXCHANGEtraded and OVERTHECOUNTER contracts, and can be structured as AMERICAN OPTIONS, BERMUDAN OPTIONS, or EUROPEAN OPTIONS. See also PUT OPTION.