= a Power Law
"The best-known power law is probably the Pareto principle, which is otherwise known as the "80/20 law." It's been overused throughout the years; Pareto's actual law only said that 80% of the wealth would be held by 20% of the population.
However, it offers a fine example of how power laws work. They generally describe a discrepancy between intensity and population: inevitably, some people do a lot more of the work in any social situation." (http://www.lifewithalacrity.com/2009/03/power-laws.html?)