Gamma explains why the SP500 Index tends to stuck at all-time highs and why it flash crashes if things turn south. Gamma is the first derivative of the option delta in the Black-Scholes model. In simple words, Gamma describes the sensitivity of the delta in relation to price movements of the underlying security. Options dealers typically maintain a delta neutral position which means that at any moment their hedging activity is determined by Gamma. A gamma flip is an event when the dealer's Gamma changes sign. For example, if Gamma flips from a positive to negative value then hedging flips from Buy to Sell. In a bull market, the majority of large investors own equities. To get some additional returns out of the existing positions they sell Calls above the current market level. This additional income is generated through the option premium paid by the options dealers. At the same time, these large players buy Puts as crash protection. In this scenario, the investors are