Dark data is the unused info hiding in your systems—think old emails, unused...

https://atomic-wiki.win/index.php/Komprise_Analysis_vs_Other_File_Analytics_Tools:_What_Sets_It_Apart%3F

Dark data is the unused info hiding in your systems—think old emails, unused files, and forgotten docs. Around 55% of data stored falls into this category, silently increasing storage costs and security risks