In a switching circuit, the idea is to simulate, as near as possible, the ideal switch having the properties of open circuit when off, <answer>short circuit</answer> when on, and an instantaneous transition between the two states. Parameters are chosen such that the "off" output is limited to leakage currents too small to affect connected circuitry; the resistance of the transistor in the "on" state is too small to affect circuitry; and the transition between the two states is fast enough not to have a detrimental effect.
What is a switching circuit trying to simulate when on?
short circuit