Galois extension
In mathematics, a Galois extension is an algebraic field extension "E"/"F" that is normal and separable; or equivalently, "E"/"F" is algebraic, and the field fixed by the automorphism group Aut("E"/"F") is precisely the base field "F". The significance of being a Galois extension is that the extension has a Galois group and obeys the fundamental theorem of Galois theory.