Residue field degree of a local field (reviewed)

Let $L/K$ be an extension of $p$-adic fields. Let $\kappa$ be the residue field of $K$ and let $\lambda$ be the residue field of $L$. The residue field degree $f$ of $L/K$ is the degree of the field extension $\lambda/\kappa$.

The base residue field degree $f_0$ of $L/K$ is the residue field degree of $K/\Q_p$. The absolute residue field degree $f_{\mathrm{abs}}$ of $L/K$ is the residue field degree of $L$ over $\Q_p$.