A fire hydrant is a pipe that allows water to flow from a water main with the control of a valve in order to put out a fire. Above-ground fire hydrants originated in the 1800s, but the underground fire hydrant was used in Asia and Europe as far back as the 1700s. In the United States, a fire hydrant may also be called a "fire plug" or a "Johnny pump," depending on the region.

A firefighter connects a fire hose to the fire hydrant and releases a valve to get water from the water main. The different valves on a fire hydrant allow it to be attached to different water sources that may be either pressurized or not pressurized.