What is a DOI?
A digital object identifier or DOI (meaning a digital identifier of an object) is a unique code assigned by a DOI registration agency in order to identify a document or other material. DOIs are most commonly assigned to online documents.
All DOI numbers begin with a 10 and contain a prefix and a suffix separated by a slash.
Examples of DOIs:
Some referencing styles recommend that you include the DOI as part of your reference if you have it. APA referencing uses DOI instead of a web address when possible.