Dark data is the information your company collects but doesn’t use or manage....

https://post-wiki.win/index.php/What_Are_Transparent_File_Tables_and_How_Do_They_Work%3F

Dark data is the information your company collects but doesn’t use or manage. It often makes up 55% of data stored, leading to wasted storage and backup costs. Plus, it increases ransomware and breach risks since unmanaged data is harder to protect