What is a car's choke?

What is a car's choke?
It is a simple butterfly valve in the top of a carburetor, which restricts the air flowing into the engine , thus increasing its velocity and enhancing the venturi effect on the fuel jets, giving the engine more fuel for cold starting. They are either manually operated , or are automatically (electrically switched via a temperature sensor). Some automatic chokes work by a wax pellet - which is solid when the engine is cold, keeping the choke closed. As the engine reaches operating temperature, the wax melts and activates a spring and lever which opens the choke. Another type has a helical spring, a bit like a clockspring, connected to the butterfly's pivot in the middle. Thermal expansion in the spring will rotate the pivot and open the choke.