Zipf

Zipf’s law is an empirical law stating that when a set of measured values is sorted in decreasing order, the value of the nth entry is often approximately inversely proportional to n.

The best-known instance of Zipf’s law applies to the frequency distribution of words in a text or corpus of natural language.

It is usually found that the most common word occurs approximately twice as often as the next common one, three times as often as the third most common, and so on.