delta is dynamic: it changes not only as the underlying stock moves, but as expiration approaches. Gamma is the Greek that determines the amount of that movement.

Gamma
Again, delta is dynamic: it changes not only as the underlying stock moves, but as expiration approaches. Gamma is the Greek that determines the amount of that movement.
Gamma is the amount a theoretical option’s delta will change for a corresponding one-unit (point) change in the price of the underlying security. In other words, if you look at delta as the “speed” of your option position, gamma is the “acceleration”. Gamma is positive when buying options and negative when selling them. Unlike delta, the sign is not affected when trading a call or put.
Just like when you buy a car, you may be attracted to more gamma/acceleration when buying options. If your option has a large gamma, its delta has the ability to approach one hundred (or 1.00) quickly, giving its price one-to-one movement with the stock. Option beginners usually see this as positive, but it can be a double-edged sword. When you have a large gamma, the delta can be affected very quickly, which means so will the option’s price. If the stock is moving in your favor, that’s great. If it’s doing an about-face and moving opposite to your prediction, changes in your option’s price may cause a lot of pain.
Gamma is highest for near-term ATM strikes, and slopes off toward ITM, OTM, and far-term strikes. This makes sense if you think it through: an option that’s ATM and close to expiration has a high likelihood to accelerate to the finish in either direction.