Gamma displays the percentage change in delta for a 1% move in the underlying.
If delta measures the speed of an option’s price change, gamma can be thought of as the acceleration of price change. An option with a high gamma is one where its delta is changing rapidly. This means it has to be re-hedged more frequently.
For most options it is only displayed as a unit of the asset, not in the base currency. However, for some, such as Best of and Worst of options it is also displayed in the base currency.