The document discusses key concepts in electric circuits including: 1. An electric circuit is a continuous conducting path for electric current to flow, consisting of wires and other resistance like a bulb connected between the terminals of a battery or cell. 2. Electric current is the flow of electric charge, usually carried by moving electrons in a wire, and is measured in Amperes. 3. Potential difference (PD) is the work done to move a unit charge between two points in a circuit, measured in Volts using a voltmeter. 4. Ohm's law states the current through a conductor is directly proportional to the PD across it for a given temperature.