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

https://astro-wiki.win/index.php/How_Does_Komprise_Discover_Dark_Data_Across_Storage_Silos%3F

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