 In this case, one has

Given a field extension "L" / "K" and a subset "S" of "L", there is a smallest subfield of "L" that contains "K" and "S".It is the intersection of all subfields of "L" that contain "K" and "S", and is denoted by "K"("S").One says that "K"("S") is the field "generated" by "S" over "K", and that "S" is a generating set of "K"("S") over "K".