Dark data is the inactive or unused information that piles up in storage—often...

https://www.wall-bookmarkings.win/dark-data-refers-to-the-inactive-or-unused-data-that-companies-keep-but-don-t

Dark data is the inactive or unused information that piles up in storage—often 60-80% of total data—yet still creates risks like ransomware exposure and contributes to $2.5 million in annual storage and backup costs