Z score
Standard Score
Standard Normal Deviate

The number of standard deviations a score is from the mean of its population. The term "standard score" is usually used for normal populations; the terms "Z score" and "normal deviate" should only be used in reference to normal distributions. The transformation from a raw score X to a Z score can be done using the following formula:

Z = (X - μ)/σ

Transforming a variable in this way is called "standardizing" the variable. It should be kept in mind that if X is not normally distributed then the transformed variable will not be normally distributed either.