Dark data is the inactive or unused information that makes up around 60-80% of...

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

Dark data is the inactive or unused information that makes up around 60-80% of enterprise storage. It often includes sensitive files forgotten over time, increasing risks like ransomware attacks and data breaches