A bestseller is a book that sells an exceptionally large number of copies in a short period of time. When a novel, biography, or other book becomes a bestseller, it means thousands or even millions of people are buying and reading it. Newspapers like The New York Times publish weekly bestseller lists ranking the most popular books, and authors dream of seeing their work reach the top spot.

The term can also describe products beyond books. A toy, video game, or album might become a bestseller if it sells far more copies than competing products. A bestselling author is someone whose books consistently sell huge numbers, like J.K. Rowling or Rick Riordan.

What makes something a bestseller varies. Sometimes it's brilliant writing, sometimes clever marketing, sometimes just lucky timing when a book captures what people are curious about. A book might become a bestseller because a celebrity recommends it, because it tackles a topic everyone's talking about, or simply because readers love it and tell their friends. Not every bestseller is a masterpiece, and not every masterpiece becomes a bestseller. Quality and popularity don't always match up, which is why some of the most celebrated books in history sold only modest numbers when they first came out.