Pure gauge

In physics, pure gauge is the set of field configurations obtained by a gauge transform on the null field configuration.So it is a particular "gauge orbit" in the field configuration's space.In the abelian case, where $A\_mu\; (x)\; ightarrow\; A\text{'}\_mu(x)\; =\; A\_mu(x)+\; partial\_mu\; f(x)$, the pure gauge is the set of field configurations $A\text{'}\_mu(x)\; =\; partial\_mu\; f(x)$ for all "f"("x").