Dark data is all the information your company collects but never really uses....

https://station-wiki.win/index.php/Why_Does_Keeping_Dark_Data_on_Flash_Storage_Feel_Like_Burning_Money%3F

Dark data is all the information your company collects but never really uses. It could be 60-80% of your stored data just sitting idle. This unused data costs businesses around $2.5 million every year in storage and management expenses