What it is:
A quartile is one of four equal parts.
How it works (Example):
For example, if we were to look at all of the closing prices for Company XYZ for every day in the last , the top 25% of those prices would represent the upper quartile of the data. The bottom 25% of those prices would represent the lower quartile of the data. There would be two quartiles in between the upper and lower quartiles. The average of all the stock prices typically falls right in the middle, between the second and third quartiles.