Dark data is the stuff companies store but rarely use—60 to 80% of their data...

https://jasperssuperbcolumn.trexgame.net/how-do-you-reduce-backup-costs-by-shrinking-primary-storage

Dark data is the stuff companies store but rarely use—60 to 80% of their data sits inactive. It matters because holding onto this unused data can cost businesses millions each year, often around $2.5 million in wasted storage and management expenses