What is a percentile in statistics?

A term used in statistics, a percentile is a data point below which a given percentage of observations in a group falls. For example, a 20th-percentile label on a score of 1340 on the Scholastic Aptitude Test means then 20 percent of test-takers scored less than that value.

For ease in reporting, percentiles are often broken into quartiles, with the 25th percentile known as the first quartile, the 50th percentile known as the median or second quartile, and the 75th percentile as the third quartile. Another option is demarcation of percentiles in 10 percent sets, known as deciles, where the 10th percentile is the first decile, and so on.