- Electricity. the opposition of inductance and capacitance to alternating current, expressed in ohms: equal to the product of the sine of the angular phase difference between current and voltage and the ratio of the effective voltage to the effective current. Symbol: XCompare capacitive reactance, inductive reactance.
- Acoustics. acoustic reactance.
- the opposition to the flow of alternating current by the capacitance or inductance of an electrical circuit; the imaginary part of the impedance Z, Z = R + i X, where R is the resistance, i = √–1, and X is the reactance. It is expressed in ohmsCompare resistance (def. 3)
- the opposition to the flow of an acoustic or mechanical vibration, usually due to inertia or stiffness. It is the magnitude of the imaginary part of the acoustic or mechanical impedance