Dark data is information your business collects and stores but doesn’t use—up...

https://direct-wiki.win/index.php/Why_Keeping_Dark_Data_on_Flash_Storage_Is_a_Bad_Idea

Dark data is information your business collects and stores but doesn’t use—up to 55% of all data. This can increase your risk of ransomware attacks and data breaches since you’re unknowingly exposing unused files