Noun

1. 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.
2. a measure of opposition to motion of something subjected to a force.
3. the sound pressure divided by the particle velocity and the surface area through which an acoustic wave propagates.
4. a measure of the opposition caused by differences between two paradigms, especially between object oriented development and relational databases
   • 1997, Bhavani M. Thuraisingham, Data Management Systems: Evolution and Interoperation (ISBN 0849394937), CRC Press, page 33:

     Some argue that having impedance mismatch is difficult for programming intensive applications.

   • 2002, Jim Melton, Advanced SQL:1999: Understanding Object-Relational and Other Advanced Features (ISBN 1558606777), Morgan Kaufmann, page 353:

     But the impedance mismatch between SQL and Java was no better than between SQL and other languages.

   • 2004, Scott W. Ambler, The Object Primer: Agile Model-Driven Development with UML 2.0 (ISBN 1397805218), Cambridge University Press, page 442:

     Why does a technological impedance mismatch exist?