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

https://penelopessmartdigests.talesignal.com/posts/how-do-i-use-regex-patterns-to-find-pii-in-documents

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