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

https://www.nav-bookmarks.win/dark-data-is-the-information-your-company-collects-but-doesn-t-use-often

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