Dark data is all the information your company collects but never uses, often...

https://wiki-canyon.win/index.php/What_is_Orphaned_Data_and_How_Do_You_Deal_With_It%3F

Dark data is all the information your company collects but never uses, often hidden in files, emails, or backups. It can be 60-80% of your stored data, quietly taking up space and costing you around $2.5 million a year in wasted storage and management