Gamma is a derivative of delta: the relationship between a derivative’s price and the price of its underlying asset. Specifically, gamma is the movement of delta in regard to the price of the underlying asset.
If an option* has a large gamma, then its price movement in relation to the price movement of its underlying asset is volatile. That enhances both risk and reward, because any price move in the underlying asset will be amplified in the price move of its option.
*Options are only available via spread betting accounts and professional CFD accounts.
Spread bets and CFDs are complex instruments and come with a high risk of losing money rapidly due to leverage. 79% of retail investor accounts lose money when trading spread bets and CFDs with this provider. You should consider whether you understand how spread bets and CFDs work, and whether you can afford to take the high risk of losing your money. Spread bets and CFDs are complex instruments and come with a high risk of losing money rapidly due to leverage.