What does IQR mean in math?

Answer 1

The interquartile range (IQR) is a measure of variability, based on dividing a data set into quartiles. Quartiles divide a rank-ordered data set into four equal parts.

Answer 2

It is the inter-quartile range. The lower quartile is an observation such that a quarter of the observations are lower than it. The upper quartile is defined analogously. The IQR is the difference between the upper and lower quartiles.