Dark data is the inactive or unused information your business stores but...

https://wiki-nest.win/index.php/Tiering_vs_Archiving_%E2%80%93_What_Is_Safer_for_Inactive_Data%3F

Dark data is the inactive or unused information your business stores but doesn’t analyze. It can make up 55% of your data and often hides risks like ransomware exposure. Plus, storing and backing up this data wastes money—sometimes over $2