Dark data is operational data that is not being used. Consulting and market research company Gartner Inc. describes dark data as "information assets that organizations collect, process and store in the course of their regular business activity, but generally fail to use for other purposes."
With the growing accumulation of structured, unstructured and semi-structured data in organizations -- increasingly through the adoption of big data applications -- dark data has come especially to denote operational data that is left unanalyzed. Such data is seen as an economic opportunity for companies if they can take advantage of it to drive new revenues or reduce internal costs. Some examples of data that is often left dark include server log files that can give clues to website visitor behavior, customer call detail records that can indicate consumer sentiment and mobile geolocation data that can reveal traffic patterns to aid in business planning.
Dark data may also be used to describe data that can no longer be accessed because it has been stored on devices that have become obsolete.