On Monday 23rd April, 2012, a new International Standards Office (ISO) standard was authorised - ISO 26324:2012

DOI is an acronym for "digital object identifier".

The formal explanation from ISO is "specifies the syntax, description and resolution functional components of the digital object identifier system, and the general principles for the creation, registration and administration of DOI names.

A DOI name is an identifier of an entity - physical, digital or abstract - on digital networks. It provides information about that object, including where the object, or information about it, can be found on the Internet".

The more informal explanation is "that it is an efficient means of identifying an entity over the Internet and used primarily for sharing with an interested user community or managing as intellectual property."

You will find most journal articles & conference papers now have a DOI embedded at time of publication.

For further information, please read this article from ISO or visit the DOI Organisation.