The interquartile range (IQR) is the difference between quartiles 1 and 3 (Q1 and Q3).
The median of an ordered dataset is the central value (if the datasize is odd) or the average of the central pair of values (if the datasize is even). The median is the same as Q2 (quartile 2). Q1 is the median of the lowest value and Q2, while Q3 is the median of Q2 and the highest value. The range is the highest value (MAX) minus the lowest value (MIN) in the dataset; but IQR=Q3-Q1 which will be smaller than the range MAX-MIN. The IQR is where 50% of the data lie, leaving 25% below Q1 and 25% above Q2.