Circuitry is a network of interconnected paths through which electricity flows, especially in a computer or other electronic device. It's a bit like the electrical version of the body's circulatory system.
Circuitry can refer to the actual electronic components that direct and control the flow of electricity in a device or to the detailed plans for an electrical circuit or system of circuits. Each electrical circuit has a source of electrical power (such as a battery), a conductive pathway (such as a wire), and a load that is being powered by the electricity. A switch is opened or closed to start or stop the flow. A device's circuitry is made up of all the circuits within it as well as the pieces connecting them.