A stack of books found after cleaning a room Tsundoku (積ん読) is the phenomenon of acquiring reading materials but letting them pile up in one's home without reading them.[1][2][3][4] The term is also used to refer to books ready for reading later when they are on a bookshelf. The term originated in the Meiji era (1868–1912) as Japanese slang.[4] It combines elements of the terms tsunde-oku (積んでおく,