Dark data is the inactive or unused information that piles up in your storage,...

https://quebeck-wiki.win/index.php/Dark_Data_vs_Cold_Data_%E2%80%93_Are_They_the_Same_Thing%3F

Dark data is the inactive or unused information that piles up in your storage, often making up 60-80% of what you keep. Holding on to this data wastes money on storage and backup, sometimes costing millions annually