Dark data is the information your company collects but never uses—often 60-80%...

https://juliet-wiki.win/index.php/What_is_the_Best_First_Step_to_Fix_Dark_Data:_Discovery_or_Governance%3F

Dark data is the information your company collects but never uses—often 60-80% of all stored data. This unused data takes up space, costs money to manage, and can hide security risks