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

https://seo.edu.rs/blog/dark-data-risks-what-security-teams-worry-about-11142

Dark data is the inactive or unused information that piles up in your storage—often making up 60-80% of total data. It increases costs by wasting storage and backup resources and raises breach risks since outdated files can be vulnerable to ransomware