Dark data is the inactive or unused information stored across your...

https://mega-wiki.win/index.php/Dark_Data_and_AI_Hallucinations_%E2%80%93_Is_There_a_Connection%3F

Dark data is the inactive or unused information stored across your systems—often 60-80% of your data. It matters because it increases storage and backup costs, sometimes wasting millions annually, and raises breach risks including ransomware exposure