1. Something that delays or prevents progress, or the preventing of progress.
2. Electricity opposition to flow of alternating current; the opposition in an electrical circuit to the flow of alternating current, consisting of resistance and reactance.
3. The ratio of the pressure to the volume displacement at a given surface in a sound-transmitting medium.
4. Opposition to blood flow in the circulatory system.
5. Resistance of an acoustic system to being set in motion.
6. Etymology: formed from Latin impedire, "to entangle, to ensnare, to hinder"; literally, "to put feet into fetters"; from Latin im-, "in", and pedis, "chain for the feet" + -ance, "an action, state, condition".

A mechanical factor that determines the amount of sound energy that is absorbed or reflected at the eardrum: Auditory impedance is also related to the loss of transmission of sounds to the middle ear and the cochlea (part of the inner ear that converts mechanical energy, or vibrations, into nerve impulses sent to the brain).

The opposition to electron flow in a conducting material.

1. The total opposition to the flow of alternating current in a circuit because of resistance and reactance (a form of electric resistance observed in an alternating current).
2. The opposition which a circuit presents to electric current.

The impedance includes both resistance and reactance.

Resistance results from collisions of the current-carrying charged particles with the internal structure of the conductor while reactance is an additional opposition to the movement of an electric charge that comes from the changing electric and magnetic fields in circuits that carry alternating current.

A device that measures the complex ratio of voltage to current in a given circuit at a given frequency.

1. An instrument that uses gas-to-tissue ratio to set an alarm or to measure a volume.
2. A technique for determining blood vessel occlusion that determines volumetric changes in a limb by measuring changes in its girth as indicated by changes in the electric impedance of mercury-containing polymeric silicone tubes in a pressure cuff.