Dark data is the information companies collect but never use—often 60 to 80% of...

https://sticky-wiki.win/index.php/What_is_the_Best_First_Step_to_Fix_Dark_Data:_Discovery_or_Governance%3F

Dark data is the information companies collect but never use—often 60 to 80% of their stored data. It’s like having a cluttered attic filled with stuff that costs money to store but offers no value