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

https://www.random-bookmarks.win/dark-data-is-the-inactive-or-unused-information-that-builds-up-in-your

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