Intercom is a feature that allows you to make an announcement to one extension or a group of extensions via a phone speaker. The called party does not need to pick up the handset. It can be achieved by pressing the feature code on your phone and it is a two-way audio call.
Intercom feature can be used in some scenarios like executive environment or alarm announcement. The executive can use the intercom feature to give messages to the assistant by simply pushing a phone key. Some association can also use the intercom feature to make the alarm announcements.