A common carrier switching center in which trunks and/or loops are terminated and switched. Note: In the DOD, "common carrier" is called "commercial carrier. " Synonym switch. Other synonyms end office, exchange, local central office, local exchange, local office, switching center (except in DOD DSN usage,) switching exchange, telephone exchange. 2. A switching unit, in a telephone system which provides service to the general public, having the necessary equipment and operations arrangements for terminating and interconnecting subscriber lines and trunks or trunks only. There may be more than one central office in a building.