Dark data is the inactive or unused information companies keep without...

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

Dark data is the inactive or unused information companies keep without realizing its impact. Around 55% of stored data is dark, which leads to wasted storage and backup costs. It also increases risk, like exposure to ransomware attacks on forgotten files