impedance

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A measure of the total opposition to current flow in an alternating current circuit, made up of two components, ohmic resistance and reactance, and usually represented in complex notation as Z = R + iX, where R is the ohmic resistance and X is the reactance.
• noun An analogous measure of resistance to an alternating effect, as the resistance to vibration of the medium in sound transmission.

from The Century Dictionary.

• noun Hindrance; specifically, in electricity, an apparent increase of resistance due to induction in a circuit.
• noun Impedance is the apparent resistance of an alternating-current circuit, or the ratio of the electromotive force consumed by an alternating current, divided by the current. On account of the electromotive force consumed by self-induction, the apparent resistance with alternating currents is greater than that with direct currents, though the power-consumption is the same. The impedance consists of two components—resistance, which consumes power, and reactance, which is the wattless resistance due to self-induction. See resistance, 3, and reactance.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Elec.) The apparent resistance in an electric circuit to the flow of an alternating current, analogous to the actual electrical resistance to a direct current, being the ratio of electromotive force to the current. It is equal to R2 + X2, where R = ohmic resistance, X = reactance. For an inductive circuit, X = 2πfL, where f = frequency and L = self-inductance; for a circuit with capacity X = 1 ÷ 2πfC, where C = capacity.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics A measure of the opposition to the flow of an alternating current in a circuit; the aggregation of its resistance, inductive and capacitive reactance. Represented by the symbol Z.
• noun physics, usually with “mechanical” a measure of opposition to motion of something subjected to a force.
• noun physics, usually with “acoustic” or “sound” the sound pressure divided by the particle velocity and the surface area through which an acoustic wave propagates.
• noun by analogy, software engineering, usually with “mismatch” a measure of the opposition caused by differences between two paradigms, especially between object-oriented development and relational databases

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a material's opposition to the flow of electric current; measured in ohms