mutual inductance, \(M\)

https://doi.org/10.1351/goldbook.M04076
For two thin conducting loops, the magnetic flux through one loop, caused by an electric current in the other loop, divided by that current.
Source:
Green Book, 2nd ed., p. 15 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)