Gamma is the second derivative of the option’s price (premium) with respect to the underlying price/ rate. It is usually considered a measure of the curvature of the premium curve (that depicts the relationship between option price and underlying price).

Gamma = change in delta ÷ change in underlying price

If an option’s gamma has a negative value that means the option’s delta will change in the opposite direction with regard to the change in the underlying. Gamma is the same for call or put options if the expiration date and exercise price are the same.

Typically, gamma is negative for short option positions.