Call Option
A call option is the right, not the obligation, to buy the underlying at a strike by expiry — convex upside for a premium.
Definition
Payoff = max(S − K, 0) for a European call, paid at expiry. American can exercise early. The premium is the market’s price of that convexity, driven by spot, rates, borrow, and implied vol. Short calls have the opposite payoff and undefined left tail if naked.
Why it matters
Calls are how you buy upside with defined debit, or sell upside for income. The Greek risk is not optional.
Case
A 10-delta call into an event. If realized vol exceeds implied, the long makes money even if spot is only slightly up; if the event is a dud, theta wins for the short.
How to read it
Strike, expiry, implied vs your realized view, and whether you are long or short the call. Premium is not a stop.