Final answer:
A circuit breaker is a resettable switch that interrupts the flow of electric current to protect a circuit from damage due to overload.
Step-by-step explanation:
A circuit breaker is an automatic switch that stops the flow of electric current in a suddenly overloaded or otherwise abnormally stressed electric circuit. Unlike a fuse, which permanently breaks the connection and requires replacement, a circuit breaker can be reset. Circuit breakers contain a bimetallic strip that bends and triggers a mechanism to break the circuit when overheated, thereby preventing damage from sustained high current. This automatic switch can be restored to operation after the problem has been fixed, making it a convenient and reliable safety device in electrical systems.