Dark data is the inactive or unused information stored in your systems—about...

https://wiki-dale.win/index.php/What_Is_the_Difference_Between_Data_Catalog_and_Metadata_Index_for_Files%3F

Dark data is the inactive or unused information stored in your systems—about 60% to 80% of it just sits there. This data isn’t just taking up space; it costs money to keep and can create noise that messes up AI projects