The entropy quantity has been known for a long time now. In statistics it is the de facto measure of the dispersion of a categorical variable. Unfortunately it is rarely taught or described in statistical textbooks; for example, see its absence in Howell (1997) and Saporta (1990). It seems once again that categorical variables are thought as less than important and put aside. We hope this work will bring an increased interest in this simple, adequate yet powerful measure.