Dark data is the untapped information stored but not actively used—often making...

https://www.inter-bookmarks.win/dark-data-is-the-inactive-or-unused-information-that-sits-in-your-storage-often

Dark data is the untapped information stored but not actively used—often making up 55% of enterprise data. It drives up storage and backup costs and increases breach risk since unmanaged data is more vulnerable to ransomware