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

https://touch-wiki.win/index.php/What_Is_a_Global_Namespace_and_Does_It_Help_with_Dark_Data%3F

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 It increases costs by wasting storage and backup resources and raises breach risks since outdated files can be vulnerable to ransomware