A ball valve is a type of valve used to control the flow of liquid or gas through a pipeline. It derives its name from the hollow, perforated ball inside the valve that rotates to regulate the flow.

The valve is operated by turning a handle or lever connected to the stem, which rotates the ball within the valve body. When the handle is positioned perpendicular to the pipe, the valve is closed; when it is parallel to the pipe, the valve is open.