What term equals the ratio of AC voltage to AC current in a system or circuit?

Ohm's Law states that resistance is the ratio of voltage to current (R = V/I) in a strictly DC circuit. However, in an AC circuit, this ratio of AC voltage to AC current represents the total opposition to current flow, which includes both resistance and reactance. This combined total is called impedance (Z = V/I). Resistance only accounts for the non-reactive part of the circuit, and reactance only accounts for the frequency-dependent part. Therefore, impedance is the only comprehensive term that accurately describes the total AC voltage to AC current ratio.