long tail

A long tail is a way of describing how things are spread out. It looks a lot like a caterpillar: it starts out with a big lump at the front (the "head") and then goes on for a longer time with a lot of small lumps (the "tail") at the end. For example, in the entertainment world, there are a small number of very popular movies and songs that are known by almost everybody (the "head"), but then there are lots of movies and songs that are only known to a small number of people (the "tail"). So the long tail is a way of showing that although a few things are very popular, there are also a lot of things out there that are not as popular but still exist.