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.