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

https://www.golf-bookmarks.win/dark-data-is-the-inactive-or-unused-information-stored-across-your

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 It increases costs by wasting storage and backup resources and raises breach risks since outdated files can be vulnerable to ransomware