A ball valve is a flow control device that uses a hollow, perforated, and pivoting ball to control fluid flowing through it. It is open when the hole through the middle of the ball is in line with the flow inlet, and closed when it is pivoted 90 degrees by the valve handle, blocking the flow.

The handle lies flat in alignment with the flow when open, and is perpendicular to it when closed, making for easy visual confirmation of the valve's status. The shut position 1/4 turn could be in either a clockwise or counter-clockwise direction. Wikipedia