A percentile is a value at or below which a given percentage or fraction of the variable values lie. For a set of measurements arranged in order of magnitude, the pth percentile is the value that has p% of the measurements below it and (100-p)% above it. Thus, the 20th percentile is the value such that one fifth of the data lie below it. It is higher than 20% of the data values and lower than 80% of the data values.