Dark data is the inactive information companies store but rarely use. It can be...

https://delta-wiki.win/index.php/How_Do_I_Set_Up_Governance_Controls_Before_AI_Ingestion%3F

Dark data is the inactive information companies store but rarely use. It can be as much as 60-80% of all stored data. This unused data takes up space and costs businesses millions—sometimes $2.5 million annually—in storage and management