DICOM
Digital Imaging and Communications in Medicine
DICOM is the international standard that defines how medical images and their associated patient and acquisition data are formatted, stored and exchanged between imaging devices.
What DICOM means in practice
It covers far more than a file format. DICOM specifies the data dictionary that names every element, the network services devices use to talk to each other, the media format for a CD or USB export, and the security profiles that apply to all of it — which is why the standard is published as a set of numbered parts rather than one document. Any two devices that both implement it can exchange a study without a bespoke integration.
Source
This definition follows NEMA PS3.1 — Introduction and Overview, published by NEMA as part of the DICOM standard.
Related terms
DICOM tag
A DICOM tag is the pair of numbers — a group number and an element number — that identifies one specific data element inside a DICOM file, such as (0010,0010) for Patient's Name.
.dcm file (DICOM Part 10 file format)
A DICOM file stores one image or object using the Part 10 format: a 128-byte preamble, the four-byte prefix "DICM", and then the data elements — and the .dcm extension is a common convention, not a requirement of the standard.
PACS
A PACS is a system that stores, retrieves, distributes and displays medical images, connected to imaging modalities and viewing workstations over a DICOM network.
Transfer Syntax
A transfer syntax is the set of encoding rules — byte ordering, explicit or implicit value representation, and any compression — that a DICOM object is written in, and it is negotiated between two devices before they exchange data.
Related on this site: What a DICOM viewer is, and the three kinds.