Dark data

Dark data is the type of unstructured, untagged and untapped data that is found in data repositories and has not been analyzed or processed. It is similar to big data but differs in how it is mostly neglected by business and IT administrators in terms of its value such as user logs or customer call logs. Similar to dark matter in physics, dark data often comprises most organizations universe of information assets and organizations often retain dark data for compliance purposes only. Storing and securing data typically incurs more expense (and sometimes greater risk) than value. 
Dark data is also known as dusty data.