Call option
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
Option (finance)
In finance, an option is a derivative financial instrument that specifies a contract between two parties for a future transaction on an asset at a reference price. The buyer of the option gains the right, but not the obligation, to engage in that transaction, while the seller incurs the...

. The buyer of the call option has the right, but not the obligation to buy an agreed quantity of a particular commodity
In economics, a commodity is the generic term for any marketable item produced to satisfy wants or needs. Economic commodities comprise goods and services....

 or financial instrument (the underlying
In finance, the underlying of a derivative is an asset, basket of assets, index, or even another derivative, such that the cash flows of the derivative depend on the value of this underlying...

) from the seller of the option at a certain time (the expiration date) for a certain price (the strike price
Strike price
In options, the strike price is a key variable in a derivatives contract between two parties. Where the contract requires delivery of the underlying instrument, the trade will be at the strike price, regardless of the spot price of the underlying instrument at that time.Formally, the strike...

). The seller (or "writer") is obligated to sell the commodity or financial instrument should the buyer so decide.