In applied usage we typically take the average of values or terms which is done by summing them and dividing by the number of terms (for simple average): $$\sum_{i=1}^n \frac{a_i}{n}$$
It dawned on me that the use of this form of mixing terms over some other form might be arbitrary. Why not?: $$\sqrt[n]{\prod_{i=1}^n a_i} $$ Is this equivalent to something that is already used extensively? Does it have a name?
This is called the geometric mean of the $a_i$. Here is its Wikipedia page.