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

https://connersinterestingblog.theglensecret.com/how-do-i-keep-unknown-departmental-shares-from-becoming-dark-data-again

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