This is known as a standardised score and it often corresponds to a ‘normed’ score. The Z-Score scale ranges from approximately -3 to +3 and corresponds to the statistical distribution descriptor ‘Standard Deviation’. The Z-score also lies along a normal distribution. Individuals with a Z-Score of 0 are said to be at the 50th percentile which means they have done better (or worse) than 50% of people who have taken that assessment previously (norm group).
Z-scores are not used for any feedback of assessments, but instead tell you where an individual sits on a distribution (see ‘normal distributions’). This scale helps to derive other useful scales such as T-Scores, Stens etc.