Wikipedia
"Tsundoku" (n.) is the condition of acquiring reading materials but letting them pile up in one's home without reading them. "Tsundoku" originated as Japanese slang "tsun-doku". 「積ん読」 came from 「積んでおく」 "tsunde-oku" (to pile things up ready for later and leave) and 「読書」 "dokusho" (reading books). 「積んどく」 "tsundoku" is a euphonic change of 「積んでおく」. It is also used to refer to books ready for reading later when they are on a bookshelf. As currently written, the word combines the characters for "pile up" and the character for "read" .
A. Edward Newton is quoted as saying: "Even when reading is impossible, the presence of books acquired produces such an ecstasy that the buying of more books than one can read is nothing less than the soul reaching towards infinity ... we cherish books even if unread, their mere presence exudes comfort, their ready access reassurance."12