Gamma
Rate of change of delta with respect to underlying price. The second derivative of option value.
Gamma is an options Greek measuring how fast an option’s delta changes as the underlying price moves. High gamma means delta changes rapidly — the option becomes more (or less) sensitive to price quickly.
For market makers, gamma determines how much they need to hedge for each price move. Positive gamma requires selling into rallies and buying dips (stabilizing). Negative gamma requires the opposite (amplifying).
See also: GEX (Gamma Exposure), Dealer Hedging