(1.)In a system, a shared boundary, i.e., the boundary between two subsystems or two devices. (2.) A shared boundary between two functional units, defined by specific attributes, such as functional characteristics, common physical interconnection characteristics, and signal characteristics. (3.) A point of communication between two or more processes, persons, or other physical entities. (4.) A point of interconnection between user terminal equipment and commercial communications facilities. (5.) To interconnect two or more entities at a common point or shared boundary.^[1]