A bar valve is a type of valve that is used to control the flow of liquids or gases. It is typically made of metal and consists of a handle, stem, and seat. The handle is used to open and close the valve, while the stem and seat regulate the flow of the liquid or gas. The term 'bar valve' comes from the fact that it is often used in bars to control the flow of beer or other beverages. TAP is a three-letter word that is used to describe the action of opening and closing a bar valve.