Dark data is the inactive or unused information stored away and overlooked,...

https://www.cool-bookmarks.win/dark-data-is-the-stuff-your-company-collects-but-rarely-uses-up-to-55-of-all

Dark data is the inactive or unused information stored away and overlooked, making up about 60%-80% of most companies’ data. This hidden stash isn't just costing money—it creates risk and adds noise that can confuse AI projects