Dark data is the information your company collects but doesn’t use, often...

https://city-wiki.win/index.php/How_Do_I_Make_NAS_and_Object_Storage_Searchable_Like_Google%3F

Dark data is the information your company collects but doesn’t use, often making up 55% or more of your stored data. It increases storage and backup costs and raises breach risk since outdated data can be a prime target for ransomware