/im peed"ns/ , n.
1. Elect. the total opposition to alternating current by an electric circuit, equal to the square root of the sum of the squares of the resistance and reactance of the circuit and usually expressed in ohms. Symbol: Z
2. Also called mechanical impedance . Physics. the ratio of the force on a system undergoing simple harmonic motion to the velocity of the particles in the system.
3. something that impedes; an obstacle or hindrance.
[ 1886; IMPEDE + -ANCE; term introduced by O. Heaviside ]