What does the interquartile range describe?

1. The quartiles split an ordered data set into four groups of equal size. 2. The interquartile range is found by subtracting the first quartile from the third quartile. 3. That subtraction gives the range of the middle half of the data set. 4. Halving it gives the semi interquartile range, which is a separate measure again. _Source: Siyavula Mathematics Grade 10 (Everything Maths, CC BY 4.0), Chapter 10: Statistics_