Source : Free On-Line Dictionary of Computing

root bridge
     
         A {bridge} which
        continuously transmits {network} {topology} information to
        other bridges, using the {spanning tree protocol}, in order to
        notify all other bridges on the network when topology changes
        are required.
     
        This means that a network is able to reconfigure itself
        whenever a network link (e.g. another bridge) fails, so an
        alternative path can be found.  The presence of a root
        bridge also prevents {loops} from forming in the network.
     
        The root bridge is where the paths that {frames} take through
        the network they are assigned.  It should be located centrally
        on the network to provide the shortest path to other links on
        the network.  Unlike other bridges, the root bridge always
        forwards frames out over all of its {ports}.
     
        Every network should only have one root bridge.  It should
        have the lowest bridge ID number.
     
        (2000-11-26)