Dark data is the information stored but not actively used, often making up 55%...

https://highstylife.com/why-do-rag-pipelines-get-worse-when-you-add-more-documents/

Dark data is the information stored but not actively used, often making up 55% of corporate data. This unused data increases storage and backup costs and raises breach risk by expanding your attack surface. It can also expose you to ransomware attacks