A call option is a financial instrument that gives the holder the right, but not the obligation, to buy the underlying asset at a predetermined price, known as the strike price. The holder of a call option has the right to exercise the option and buy the underlying asset at the strike price, but is not required to do so.

Here are some key characteristics of call options:

1. Right to buy: The holder has the right to buy the underlying asset.

2. Strike price: The predetermined price at which the holder can buy the underlying asset.

3. Expiration date: The last day on which the option can be exercised.

4. Premium: The price paid by the holder to acquire the option.

5. Underlying asset: The security or asset that the option is based on.

Call options are often used for various purposes, including:

1. Speculation: To bet on price increases in the underlying asset.

2. Hedging: To lock in a purchase price for an asset needed in the future.

3. Income generation: To sell options and collect premiums.

4. Spreads: To combine options with different strike prices or expiration dates.

Remember, call options give the holder the right to buy, but not the obligation, so the holder can choose to exercise the option or let it expire worthless.