What is Geometric mean?

The n-th root of the product of n positive numbers. It is especially needed for averaging growth rates: each year's growth is multiplied by the previous year's result, not added to it. That is why the simple arithmetic mean of percentage growth rates overstates the true average rate, while the geometric mean gives the constant annual rate that leads exactly from the initial value to the final value. In business this indicator is also called the "compound annual growth rate" (CAGR). For positive numbers the geometric mean is never greater than the arithmetic mean; the two are equal only when all the numbers are equal.

Source: Britannica: geometric mean