Dark data is all the information companies collect but never use—like old...

https://smart-wiki.win/index.php/What_Is_Orphaned_Data_and_How_Do_You_Deal_With_It%3F

Dark data is all the information companies collect but never use—like old emails, logs, or forgotten files. It can make up 60-80% of stored data, costing organizations up to $2.5 million every year in storage and management