1. Circuit: A circuit is a closed conducting path through which an electric current either flows or intended to flow. A circuit consists of active and passive elements in it.

2. Linear Circuit: A circuit whose parameters are constant with time and they don’t change with voltage or current and they obeys Ohm’s law.

3. Non-linear Circuit: It is that circuit whose parameters change with voltage or current.

4. Bilateral Circuit: A bilateral circuit is one whose properties are the same in either direction. Example, a transmission line & parameter such as resistor, inductor & capacitor.

5. Unilateral Circuit: It is a circuit whose properties change with the direction of its operation. Example such as diode, triode , transistor & SCR.

6. Active Network: is a network which contains one or more than one source of emf along with passive element.

7. Passive Network: is one which contains no source of emf.

8. Node: is a point in a circuit where two or more circuit elements are connected together.

9. Branch: is the part of a network which lies between two nodes.

10.Loop: It is a close path in a circuit in which no element or node is encountered more than once.

11.Mesh: It is a loop that contains no other loop within it.

It should be noted that, unless stated otherwise, an electric network would be assumed passive.

There are two general approaches to network analysis:

i. Direct Method

ii. Network Reduction Method

Direct Method: Here the network is left in its original form while determining its voltages and currents.

e.g.: Loop Analysis, Nodal Analysis, Superposition Theorem, Compensation Theorem, and Reciprocity Theorem.

Network Reduction Method: Here, the original network is converted into a much simpler equivalent circuit for rapid and easy calculation.

e.g.: Delta/Star and Star/delta Conversions, Thevenin’s Theorem and Norton’s Theorem.