i) Unilateral circuit: If the characteristic, response or behavior of circuit dependents on the direction of flow of current through its elements, then the circuit is called as a unilateral circuit. e.g. networks containing elements like diodes, transistors, thyristors etc.
ii) Bilateral Circuit: If the characteristic of circuits (response or behavior) is independent of the direction of current through its elements in it, then the circuit is called as a bilateral circuit e. g. circuits containing elements like resistances, inductances and capacitances.