Source : WordNet®

central office
     n : (usually plural) the office that serves as the
         administrative center of an enterprise; "many companies
         have their headquarters in New York" [syn: {headquarters},
          {main office}, {home office}, {home base}]

Source : Free On-Line Dictionary of Computing

central office
     
         The place where telephone companies terminate
        customer lines and locate switching equipment to interconnect
        those lines with other networks.
     
        (1995-03-20)