Dark data is all the inactive information your company stores but never...

https://spark-wiki.win/index.php/What_Is_Bucket_Sprawl_and_Does_It_Create_Dark_Data%3F

Dark data is all the inactive information your company stores but never uses—often 60-80% of your data. It quietly eats up storage space and can cost businesses up to $2.5 million each year in wasted resources