A circuit breaker is an electromechanical device that carries out a very similar job as a fuse. They are designed to make circuits under normal conditions and to break circuits in the event of an overload, .e.g. a short circuit.
The key difference between a fuse and a circuit breaker is that once a fuse has performed it duty it needs to be replaced, whereas a circuit breaker can be reset.
Modern electricity supplies use circuit breakers rather than fuses and these will be located at different locations in a building.
In the event of a circuit breaker 'tripping' and cutting power, then this will allow an engineer to check the equipment for any faults before the circuit breaker can be safely reset.
Another advantage of circuit breakers is that they can be switched off manually to allow safe repair and maintenance.