Dark data is the inactive or unused information stored across your systems,...

https://wiki-legion.win/index.php/Why_Do_RAG_Pipelines_Get_Worse_When_You_Add_More_Documents%3F

Dark data is the inactive or unused information stored across your systems, often making up 55% of all data. It poses a real risk by increasing exposure to ransomware and breaches and drives up storage and backup costs, sometimes wasting millions annually