A best seller is a book that thousands of people are buying and reading. Most authors dream of seeing their books end up on best seller lists.
Some books are read by a small number of people, and others become very popular, flying off the shelves as soon as bookstores can stock them. Newspapers and magazines use sales data to publish best seller lists which are often divided into categories — a book could be a science fiction, young adult, or nonfiction best seller, for example. Strictly speaking, the all-time best seller is the Bible, which has sold an estimated five billion copies.