Dark data is unused information that often sits idle—about 55% of enterprise...

https://www.yankee-bookmarkings.win/dark-data-is-the-information-your-company-collects-but-doesn-t-use-or-manage

Dark data is unused information that often sits idle—about 55% of enterprise data remains dark. This dormant data poses a real breach risk if hacked and adds unnecessary storage and backup costs, which can exceed $2.5 million annually