Dark data is the information your company collects but doesn’t use—often 55% or...

https://sierra-wiki.win/index.php/Why_Do_We_Keep_Paying_to_Back_Up_Data_Nobody_Uses%3F

Dark data is the information your company collects but doesn’t use—often 55% or more of stored data. This inactive data increases storage and backup costs and raises breach risks, including ransomware targets hidden in forgotten files