Dark data is the information stored but not actively used, often making up 55%...

https://mag-wiki.win/index.php/Dark_Data_in_Object_Storage_%E2%80%93_Why_Do_Buckets_Get_Out_of_Control%3F

Dark data is the information stored but not actively used, often making up 55% of corporate data. This unused data increases storage and backup costs and raises breach risk by expanding your attack surface. It can also expose you to ransomware attacks