A tap is a valve for controlling the flow of a liquid or gas (gas-tap). It can refer to a valve for tap water (a faucet) or a valve connected to a keg of beer to allow one to control the flow of the beverage, also called a beer tap. In a broader but less common sense, it may refer to any water spigot.

Older style water taps for bathing, sinks and basins generally had separate hot and cold taps. A more modern tap design is the 'mixer', a single tap whose handle moves up and down to control the amount of water flow and from side to side to control the temperature of the water (achieved by mixing the hot and cold water together). Latest designs do this using a built in thermostat.