Dark data is the unused or forgotten information stored in your systems, often...

https://holdensimpressivethoughts.lumenforgex.com/posts/how-many-sensitive-data-scanners-do-teams-usually-need

Dark data is the unused or forgotten information stored in your systems, often making up 55% of your data. It’s costly because it wastes storage and raises security risks. For AI projects, dark data adds noise, slowing down results