In electromagnetism, the Lorenz gauge condition is the gauge fixing in which
where 
is the four-potential, the comma denotes a partial differentiation and the repeated index indicates that the Einstein summation convention is being used.
This gauge has the advantage of being Lorentz invariant. It still leaves some residual gauge degrees of freedom, but they propagate freely at the speed of light, so they are insignificant.
The Lorenz gauge is often erroneously spelled as 'Lorentz gauge', many people believing that H. Lorentz, a Dutch physicist, was the first to state the condition. In fact, it was the Danish physicist Ludwig Lorenz who first published this condition.
See also Coulomb gauge, Weyl gauge
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