The “Greeks” are named after Greek letters because that's how they show up in the Black-Scholes math. But you don't need the math to use them — each one has a plain-English meaning in dollars.
Delta (Δ) — the directional exposure
Dollars your P&L changes per $1 move in the underlying. A long call has positive delta (you make money when the stock goes up); a long put has negative delta (you make money when the stock goes down). A delta of 54 means: SPY goes up $1, you gain about $54.
Gamma (Γ) — how fast delta changes
How much your delta shifts per $1 spot move. High gamma means your directional exposure changes quickly — a small rally can turn a slightly-bullish position into a strongly-bullish one. Gamma peaks near the strike and fades away from it.
Theta (Θ) — the daily bleed
Dollars gained or lost per calendar day from time decay. Negative for long options (you pay for time), positive for short options (you collect it). If your theta is −$22.49, you'll lose about $22 tomorrow if nothing else changes.
Vega — the volatility knob
Dollars per 1 vol-point move in implied volatility. Positive vega = you benefit from rising IV. Negative vega = you benefit from IV crush. Earnings, Fed announcements, and other event risks move vega positions the most.
Rho (ρ) — the interest-rate sensitivity
Dollars per 1% move in the risk-free rate. Usually the smallest Greek for short-dated options. Matters mostly for LEAPs (long-dated options) and shifts in the yield curve.
Which one matters when?
- Directional bet: watch delta (and gamma if you might be wrong).
- Selling premium (theta plays): watch theta and gamma together.
- Trading around events: watch vega — the IV crush after earnings is real.
- LEAPs / long-dated bets: rho starts to matter, so does re-computing all of the above regularly.