Bilateral Network: An element whose response is independent of direction of current flowing through it is called Bilateral element and the network, which contains only bilateral elements, is called bilateral network.
OR
A network whose electrical characteristic or response is independent of the direction of current flowing through it, is called bilateral network.
Unilateral Network: An element whose response depends on the direction of current flowing through it, is called Unilateral element and the network, which contains at least one unilateral elements, is called unilateral network.
OR
A network whose electrical characteristic or response depends on the direction of current flowing through it, is called unilateral network.