A man using an intercom.
intercom definition by Webster's New World
intercom definition by American Heritage Dictionary
Origin: Short for intercommunication.
intercom - Computer Definition
An abbreviation of intercommunication, an intercom system is a closed (i.e., not networked) system that allows members of a group to converse with each other. An intercom system can be standalone, although Centrex systems, key telephone systems (KTSs), and PBXs commonly feature intercom capabilities. See also Centrex, KTS, and PBX.