• a set of protocols for devices communicating over a network
• the syntax and semantics of commands and associated information that can be exchanged using these protocols
• a set of media storage services and devices claiming conformance to the standard, as well as a file format and a medical directory structure to facilitate access to the images and related information stored on media that share information.

The standard was developed jointly by ACR (the American College of Radiology) and NEMA (the National Electrical Manufacturers Association) as an extension to an earlier standard for exchanging medical imaging data that did not include provisions for networking or offline media formats.

A Non-Technical Introduction to DICOM
Published by the Radiological Society of North America.

The DICOM Standard
Published by the National Electrical Manufacturers Association. (pdf)