THE GREEKS OVERVIEW
Plain English
The Greeks are your option's dashboard. Delta tells you directional exposure, Theta tells you time decay, Vega tells you volatility sensitivity, and Gamma tells you how fast Delta changes. Together, they give you a complete picture of your risk.
Going deeper
The Greeks are partial derivatives of the options pricing model that measure different dimensions of risk. Delta measures directional risk (how much the option price changes per $1 move in the stock). Gamma measures the rate of change of Delta. Theta measures time decay (how much value the option loses each day). Vega measures sensitivity to implied volatility changes. Rho measures sensitivity to interest rate changes (usually minor). Understanding the Greeks is what separates informed traders from gamblers.
Examples
Delta in Action
You own a Call with a Delta of 0.50. If the stock goes up $1.00, your option increases by $0.50 ($50 per contract). If you own 10 contracts, your position acts like 500 shares of stock (10 x 50 delta = 500).
Vega and Volatility
Your option has a Vega of 0.15. If implied volatility increases by 1 percentage point, your option gains $0.15 ($15 per contract). Before earnings, rising IV can make your options more valuable even if the stock hasn't moved.