Dark data is the inactive, unstructured information most companies don’t manage...

https://www.foxtrot-bookmarks.win/dark-data-is-the-inactive-or-unused-information-stored-but-not-analyzed-making

Dark data is the inactive, unstructured information most companies don’t manage well—often 55% of all stored data. This hidden data boosts storage and backup costs and raises risks like ransomware exposure or breaches