absolute Galois group

Let $k$ be a field. The absolute Galois group $G_{k}$ of $k$ is the Galois group $\operatorname{Gal}(k^{\operatorname{sep}}/k)$ of the field extension $k^{\operatorname{sep}}/k$ , where $k^{\operatorname{sep}}$ is the separable closure of $k$ .