Z-score: A z-score measures how many standard deviations an observation or data point is from the mean in a standard normal distribution.
Empirical Rule: The empirical rule states that for any bell-shaped curve, approximately 68% of the data falls within one standard deviation of the mean, 95% falls within two standard deviations, and 99.7% falls within three standard deviations.
Normal Distribution: A normal distribution is a bell-shaped probability distribution where most values cluster around the mean, symmetrically decreasing as they move further away from it.