The term comes from the English and is composed of the two words best for best and sell for sell together. A bestseller is therefore something that sells best. Since the word is almost exclusively applied to books, a bestseller is a book that is sold very quickly. That a book is bought by many may have different causes. In any case, the subject of the book must interest many people and be written so that many people find it exciting. A book that describes a special subject and is very complicated or little entertaining, it will therefore be difficult to become a best seller. The term generally says only about the sales figures and nothing about the quality of the book.
The sales or sales figures of books can be compared, because they are recorded by the book trade world-wide in a written overview. Bestseller is a book when it has been sold over 100,000 times in this comparison.