Dark data is the inactive or unused information that piles up in your...

https://smart-wiki.win/index.php/Dark_Data_in_Object_Storage_-_Why_Do_Buckets_Get_Out_of_Control%3F

Dark data is the inactive or unused information that piles up in your storage—up to 60-80% of it. This data not only wastes money on storage and backups but also increases your risk of ransomware attacks and data breaches