Impedance is a measure of the opposition to the flow of alternating current (AC) in a circuit. It is a complex quantity with both magnitude and phase, and is typically measured in ohms (). Impedance is determined by the resistance, inductance, and capacitance of the circuit.
Impedance is important because it affects the flow of current in a circuit. A high impedance can limit the current flow, while a low impedance can allow more current to flow. This can have a significant impact on the performance of electronic devices.