PACS
Picture Archiving and Communication System
A PACS is a system that stores, retrieves, distributes and displays medical images, connected to imaging modalities and viewing workstations over a DICOM network.
What PACS means in practice
The four verbs are the whole job: a modality sends a completed study in, the archive keeps it, a viewer asks for it back, and the network carries it both ways. "PACS" describes that role rather than any single product — the same function can be a hospital-wide archive on dedicated hardware or a single device on a clinic bench.
Source
This definition follows NEMA PS3.1 — Introduction and Overview, published by NEMA as part of the DICOM standard.
Related terms
C-STORE
C-STORE is the DICOM network service used to transfer a composite object — an image or similar instance — from one device to another, and it is the operation behind "sending a study" to a PACS.
Query/Retrieve (C-FIND and C-MOVE)
Query/Retrieve is the pair of DICOM services used to search what a remote device holds and then pull matching studies from it: C-FIND performs the search and C-MOVE transfers the results.
Storage SCP
A Storage SCP is the role a device plays when it accepts incoming DICOM images, listening for C-STORE requests and storing what it receives — the role a PACS or an archiving viewer performs.
Modality Worklist
A Modality Worklist is the DICOM service that lets an imaging device query a scheduled list of patients and procedures from a worklist provider, so demographics do not have to be typed in again at the scanner.
Related on this site: How SoftDicom acts as a PACS server.