Ciro Santilli A different and more elegant way to express Maxwell's equations by using the:instead of the:
There are several choices of electromagnetic four-potential that lead to the same physics.
E.g. thinking about the electric potential alone, you could set the zero anywhere, and everything would remain be the same.
The Lorentz gauge is just one such choice. It is however a very popular one, because it is also manifestly Lorentz invariant.
Alternative to the Lorentz gauge, but less used in general as it is not as nice for relativity invariance.