Call option
An option giving its buyer the right, but not the obligation, to buy an asset at a fixed strike price on or before a set expiry date.
The buyer of a call option pays a premium for the right to buy the underlying asset at the strike price. If the asset's price rises above the strike, the call gains value, because it lets the holder buy below the market price. If the price stays at or below the strike until expiry, the call expires worthless and the buyer loses the premium. At expiry the buyer breaks even when the asset's price equals the strike plus the premium paid. Calls give leveraged exposure: a modest rise in the asset can produce a much larger percentage gain on the premium.
For the buyer, the maximum loss is the premium, but losing it is common, because the asset has to rise by enough, soon enough. The seller of a call receives the premium and takes on the obligation to deliver the asset at the strike price if the option is exercised. A covered call, written by someone who owns the asset, gives up gains above the strike in return for income. A naked call, written without owning the asset, is among the riskiest positions an investor can take: losses can be large, can far exceed the premium received and are unlimited in theory, because there is no ceiling on how high a price can go.
General education, not personal financial, tax or legal advice.