How many standard deviations away from average you are, in one number.
means A standardized score that tells you how far a data point sits from the mean, measured in units of standard deviation—useful for comparing apples and oranges on the same scale.
from Formalized by statistician Karl Pearson in the early 1900s as part of the normal distribution toolkit; the 'z' likely borrowed from the mathematical convention of using z for standardized variables, though its exact naming origin is debated among statisticians.
college admissions testing — SAT and ACT scores converted to z scores for fair comparison across test versions and years
climate anomalies — Global temperature departures measured as z scores to show how extreme each year is relative to the baseline
baseball performance — WAR calculations use z scores to compare hitters and pitchers with wildly different statistics