Dark data is the 55% of stored information that sits unused but still costs...

https://charlie-wiki.win/index.php/We_Pay_for_300TB_and_3.5PB_in_Cloud_Storage_%E2%80%93_How_Much_Is_Junk%3F

Dark data is the 55% of stored information that sits unused but still costs money to keep and backup. It can increase your risk of ransomware attacks since unmonitored data is an easy target