Call option
A contract giving its buyer the right, but not the obligation, to buy 100 shares of the underlying stock at the strike price on or before expiration. The buyer pays a premium for that right; the seller receives the premium and takes on the obligation to deliver shares if assigned.
A call option is the natural starting point of the options market: it converts a bullish view into a defined-cost position. Its value at expiration is the greater of zero and the stock price minus the strike, which is why buyers can never lose more than the premium paid while sellers face potentially large losses on naked positions.
Before expiration a call also carries extrinsic value, so it can be profitable to sell it back well before the stock ever reaches the strike.
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