Impedance may refer to:

• the ratio of the voltage phasor to the electric current phasor, as in
  • Electrical impedance, a measure of opposition to time-varying electric current in an electric circuit.
  • Characteristic impedance, a measure of opposition to electric current propagation in a transmission line.
• Impedance matching and Impedance mismatch.
• Vacuum impedance, a universal constant.
• Electromagnetic impedance, a constant related to electromagnetic wave propagation in a medium.
• Mechanical impedance, a measure of opposition to motion of a structure subjected to a force.
• Acoustic impedance, a constant related to the propagation of sound waves in an acoustic medium.
• Linear response function, a general way to represent the input-output characteristics of a system.
• Object-relational impedance mismatch, difficulties encountered when a relational database management system in an object-oriented programming language

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