A percentile indicates the value below which a given percentage of observations fall.

The percentile rank of a score is the percentage of scores in the distribution that are equal to or lower than it.

Quartiles divide data into four equal parts: Q1 (25th percentile), Q2/Median (50th), Q3 (75th).

IQR (Interquartile Range) = Q3 - Q1, used to identify outliers.