Impedance

Impedance is the term used to represent the resistance of a circuit to alternating current, which is what comes out of amplifiers. Impedance is expressed as a value in Ohms, just like direct current resistance, but consists of the direct current resistance + capacitive and inductive reactance. These cannot be measured with a simple resistance meter.

Loudspeakers have an impedance rating which will be higher than their resistance as measured with a meter.