Dark data is the inactive or unused information that piles up in your...

https://bravo-wiki.win/index.php/What_Are_Egress_Costs_and_Why_Do_They_Matter_for_Dark_Data%3F

Dark data is the inactive or unused information that piles up in your storage—often making up 55% of all enterprise data. This unused data increases costs through wasted storage and backups, and it raises your risk of breach or ransomware exposure