Dark data is the inactive or unused information your business keeps, often...

https://telegra.ph/How-Do-I-Quantify-What-Dark-Data-Is-Costing-Us-Each-Year-07-20

Dark data is the inactive or unused information your business keeps, often making up 60-80% of stored files. It raises breach and ransomware risks since unused data is less monitored. It also leads to storage and backup waste, costing millions annually