Dark data is the huge chunk of company info—often 55% or more—that sits unused...

https://wiki-wire.win/index.php/Why_Is_Our_Backup_Taking_Longer_Every_Month%3F

Dark data is the huge chunk of company info—often 55% or more—that sits unused and forgotten. It wastes up to $2.5 million yearly on storage and adds risk by cluttering security checks