The geometric mean is a type of average that is calculated by multiplying together a set of numbers and then taking the nth root of the product, where n is the number of values in the set.

For example:
If you have a set of three numbers 2, 4, and 8, the geometric mean would be calculated as follows:
Multiply the three numbers together: 2 x 4 x 8 = 64
Take the cube root of the product: cube root of 64 = 4
Therefore, the geometric mean of the set 2, 4, and 8 is 4.

The geometric mean is useful when dealing with data that has a wide range of values or when the data is skewed. It is often used in financial calculations, such as calculating the average rate of return on an investment over multiple years.