QUARTILES
The three points on the scale of observation ( or values of the variable) which divide the total frequency into four equal parts are called quartiles for the data arranged in ascending or descending order of magnitude.
When the data are in ascending order then first point is called first quartile and is denoted by Q the second point is called second quartile and is denoted by Q_{2} which is equivalent to median and the third points is called third quartile and is denoted by Q_{3}.