Dark data is the vast amount of information companies store but never use—up to...

https://wiki-wire.win/index.php/What_Does_%22Data_Stays_Where_It_Lives_Until_Needed%22_Mean_in_Practice%3F

Dark data is the vast amount of information companies store but never use—up to 80% can sit inactive. It matters because this unused data costs businesses around $2.5 million every year in storage and management