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

https://victor-wiki.win/index.php/What_Are_Common_Examples_of_Dark_Data_at_Work%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