Mean square
In mathematics and its applications, the mean square is defined as the arithmetic mean of the squares of a set of numbers or of a random variable, or as the arithmetic mean of the squares of the differences between a set of numbers and a given "origin" that may not be zero.
When the mean square is calculated relative to a given "target" or "correct" value, or as the mean square of differences from a sequence of correct values, it is known as mean squared error.
The square root of a mean square is known as the root mean square, and can be used as an estimate of the standard deviation of a random variable.
The second moment, is also called the mean square.
