Tsundoku (Japanese: 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 tsunde-oku (積んでおく, to pile things up ready for later and leave) and dokusho (読書, reading books). As currently written, the word combines the characters for "pile up" (積) and the character for "read" (読). There are suggestions to include the word in the English language and in dictionaries like the Collins Dictionary.
The American author and bibliophile A. Edward Newton commented on a similar state in 1921.