The Mode

Shoe sizes in a group of friends: 7, 8, 8, 9, 8, 10, 7. The mode is the value that appears most often. Size 8 appears three times, more than any other, so the mode is 8.

A list can have two modes: 3, 3, 5, 6, 6 has modes 3 and 6. It can also have none at all, when every value appears exactly once. And the mode is the only average that works for things that are not numbers: if more people pick blue than any other colour, blue is the mode.

Each average answers a different question. The mean is the fair share, the median is the middle, and the mode is the most popular. A shoe shop deciding what to stock cares about the mode, because it wants the size most people buy, not an average size like 8.1 that nobody wears.