what is the definition of a z score for individual values What does its sign indicate?

A z-score measures how many standard deviations an individual value is from the mean of a dataset. It is calculated by subtracting the mean from the individual value and then dividing by the standard deviation. A positive z-score indicates that the value is above the mean, while a negative z-score indicates that it is below the mean. A z-score of zero means the value is exactly at the mean.