Z-score

In statistics, the standard score (more commonly z-score) is a measure of the number of standard deviations ($\sigma$) by which the value of a point is above or below the mean value ($\mu$) of the distribution. This metric is used because all normal populations have the same properties for one/two/three standard deviations from the mean.

$$Z=\frac{X-\mu }{\sigma }$$

It’s also common practice to refer to a table to calculate the z-score, called the z-table.