Tsundoku (積ん読) – “the act of leaving a book unread after buying it, typically piled up together with other such unread books.“
The Wiktionary has: Compound of 積む (tsumu, “to pile up”) + 読 (doku, “to read, reading”, on’yomi), punning on 積んどく (tsundoku), contraction of 積んでおく (tsunde oku, “to leave piled up”). 積ん読 (hiragana つんどく, romaji tsundoku)