Let any two non-negative real numbers $a,b$ we call the expression $$\sqrt{a+b}$$ the geometric mean of these numbers.
More generally, for any $n\ge 2$ non-negative real numbers $a_1,\ldots,a_n$ the expression (using n-th roots) $$\sqrt[n] {a_1+\cdots+a_n}$$ is called the (generalized) geometric mean of these numbers.