Tsundoku (積ん読) refers to the phenomenon of acquiring reading materials but letting them pile up in one's home without reading them. It 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. It combines elements of the terms tsunde-oku (積んでおく, "to pile things up ready for later and leave"), and dokusho (読書, "reading books"). There are suggestions to use the word in the English language and include it in dictionaries like the Collins Dictionary.
The American author and bibliophile A. Edward Newton commented on a similar state in 1921.
In his 2007 book, The Black Swan, Nassim Nicholas Taleb coined the term "antilibrary", which has been compared with tsundoku.