The Greeks are just the answers to "if ONE thing moves, how does the option's value move?" Each is a sensitivity. Five matter.
Delta — direction
Delta is how much the option gains or loses per $1 move in the stock. A delta of 0.30 means ~$0.30 per $1. It doubles as a rough hedge ratio and a rough gauge of the odds the option finishes in-the-money.
Gamma — how fast delta changes
Gamma is the curvature: how much delta itself shifts as the stock moves. It's largest near the strike and near expiry. High gamma means your exposure changes fast — great when you own options, nerve-wracking when you've sold them.
Theta — time decay (the income engine)
Theta is how much value bleeds away each day just from time passing. An option is a melting ice cube. This is the key one for us: covered-call and put-write funds sell options to collect theta — the premium that becomes their income (see PutWrite Income). The catch: sellers earn theta but take on gamma and tail risk — they get paid precisely for catching the occasional crash.
Vega and rho — volatility and rates
Vega is sensitivity to implied volatility — options get pricier when the market expects bigger swings. Rho is sensitivity to interest rates, usually the smallest of the five (but see stocks and rates).
The Greeks describe risk — they are not a crystal ball. They come straight out of the Black-Scholes framework.
Educational material — not investment advice.