A bibcock, also called a sillcock, is commonly used to provide hose connections outside of buildings, for use in gardening, watering lawns, washing cars, and so on. Certain bibcocks are colloquially known as frost-frees because they are immune to all but the worst freezing conditions. In physics and chemistry, freezing is the process of cooling a liquid to the temperature (called freezing point) where it turns solid. ...

A bibcock can be any of several valve types; commonly they have a removable control knob that pushes a rubber plug against an opening in order to close the valve. The downstream side of the valve is threaded to match standard garden hoses.

Most U.S. jurisdictions now require bibcocks to have a vacuum breaker or backflow preventer, so that water cannot return through the bibcock from the hose. This prevents contamination of the building or public water system should there be a pressure drop. An attachment commonly placed on a bibcock valve, that prevents water from being sucked backward from a garden hose into the public water system. ... A backflow prevention device is used to protect water supplies from contamination. ...