1.NounAny equipment that establishes connections between telephones.
2.NounThe rooms or building housing such equipment (a central office, as it was termed by the Bell System).
3.NounA local or locoregional network of such switched connections, of which a central office was the hub; the local company formed to create and maintain this network and its central office.
"This valley didn't have a telephone exchange until 1903, when the leading citizens of this town invested in a company to establish one."
4.NounThe portion of a telephone number representing that network, among the other networks of the larger system: the central office code. In the North American Numbering Plan, this is the "555" portion of "+1-212-555-6789".
"A: You can telephone him at 2719. B: What's the [telephone] exchange? A: LA6. I'm sorry, that's LA6-2719."