bestseller       
noun [ C ] uk/ˌbestˈsel.ər/ us/ˌbestˈsel.ɚ/
B2 畅销书
a product that is extremely popular and has sold in very large numbers
  The "Harry Potter" novels were all bestsellers. 《哈利•波特》系列小说都是畅销书。 
 the bestseller list (= the list of the most popular books) 畅销书排行榜