A fire hydrant, also called a fireplug, fire pump, johnny pump, or simply pump, is a connection point by which firefighters can tap into a water supply. It is a component of active fire protection.
A reliable source of water for the hydrant system is usually street mains and a static holding system such as a tank or reservoir with means of automatically adding water to allow.
The “hydrant” is the name for the endpoints throughout the building which firefighters can connect to. As different diameters of couplings may be used in by different fire brigades from place to place, it’s common to attach adapters to accommodate the hoses local fire fighters will use.