Dark data is the inactive or unused information that builds up in your...

https://www.sierrabookmarking.win/dark-data-is-the-inactive-information-companies-store-but-rarely-use-often

Dark data is the inactive or unused information that builds up in your storage—often 60-80% of what you keep. It increases your risk of ransomware attacks and data breaches because it’s overlooked in security scans