Digital object identifier (DOI).

A digital object identifier (DOI) is a unique string of numbers and letters specifically associated with a digital object. A digital object refers to any bit sequence with which a computer may interact. This includes images, video, sound, and text publications. DOIs are commonly used in conjunction with research and publications so that they may be used within citations. They provide a consistent, verifiable link to the original digital object, and may provide useful metadata associated with that object.