The observed values of a variable divided into hundredths. The first percentile (P1) divides the bottom 1% of values from the rest of the data set, the second percentile (P2) the bottom 2%, etc. The median is the 50th percentile (P50).
The observed values of a variable divided into tenths. The second decile is the 20th percentile, represented as either D2 or P20.
The most common type of percentile used, dividing the observed values into quarters. There are three quartiles: Q1 divides at 25%, Q2 at 50% (the median) and Q3 at 75%.