Quartiles is the four equal part of a population which is divided according to a particular variable. In statistics, Quartile divides the set of observation into 4 equal parts like how the median divides the set of observation into 2 equal parts, when arranged in the numerical order.
There are three points which divide the set of observation into 4 equal parts(as shown in the figure below). The three points are:
First or Lower quartile (Q1)
Second quartile or Median (Q2)
Third quartile or Upper quartile (Q3)