For any two real numbers $a,b$ we call the expression $$\frac {a+b}2$$ the arithmetic mean of these numbers.
More generally, for any $n\ge 2$ real numbers $a_1,\ldots,a_n$ the expression $$\frac {a_1+\cdots+a_n}n$$ is called the (generalized) arithmetic mean of these numbers.
Let $p_1,\ldots,p_n$ be positive real numbers ("weights"). Then we call the expression $$\frac {p_1a_1+\cdots+p_na_n}{p_1+\cdots+p_n}$$ the weighted arithmetic mean.
