What aspect of a circuit does the term "impedance" refer to?

Impedance specifically refers to the opposition that a circuit presents to the flow of alternating current (AC). It encompasses both resistive and reactive components of the circuit, indicating not just how much current is resisted but how reactive elements like inductors and capacitors influence current flow as well.

Impedance is typically measured in ohms and is a crucial concept in understanding how AC circuits behave. Unlike resistance, which only accounts for opposition to current flow, impedance provides a fuller picture by including phase relationships between voltage and current. This is particularly important in AC systems where these phase differences can significantly impact circuit performance.

Thus, the correct choice effectively captures the essence of what impedance represents within electrical circuits.