Digital object identifier
From Science Europe Data Glossary
Definition: a digital object identifier (DOI) is a unique and stable identifier that ensures that a digital object can be permanently found on the World Wide Web, regardless of changes in the web address (URL) where the object is found.
Explanation: a central registry ensures that the user of a DOI will be referred to its current location.
Reference: https://en.wikipedia.org/wiki/Digital_object_identifier; http://www.datacite.org/