Dark data is the inactive information companies hold but rarely use, making up...

https://fernandowehn083.timeforchangecounselling.com/how-do-i-find-dark-data-on-a-nas-without-breaking-anything

Dark data is the inactive information companies hold but rarely use, making up 60-80% of all stored data. It matters because keeping this unused data costs money—around $2.5 million per year for some businesses—while adding little value