Dark data is the 55% of stored information that companies keep but never use....

https://mill-wiki.win/index.php/S3_Intelligent_Tiering_for_Inactive_Data_%E2%80%93_What_Should_I_Watch_For%3F

Dark data is the 55% of stored information that companies keep but never use. This inactive data increases your risk of ransomware attacks and data breaches since it often lacks proper security