In AC circuits, what is the term for the total opposition to current flow?

In AC circuits, the term for the total opposition to current flow is impedance. Impedance encompasses not just the resistance (the opposition to direct current) but also accounts for the effects of capacitance and inductance present in the circuit. While resistance is a component of impedance that relates to the actual energy loss in a circuit in the form of heat, impedance represents the combined effect of resistance and the reactance, which arises from the circuit's capacitance and inductance.

Reactance, on its own, refers specifically to the opposition to current flow due to capacitive or inductive elements but does not include the resistive component. Therefore, impedance provides a more comprehensive measurement that's critical in the analysis and design of AC circuits, particularly in understanding how such circuits will behave under different conditions of frequency and load. This makes impedance a fundamental concept in electrical engineering, especially in applications involving alternating current.