Local Fields
《Local Fields》 · 第 14 页 · Chapter I，Section 4「Extensions」
When $e_{\mathfrak P}=1$ and $B/\mathfrak P$ is separable over $A/\mathfrak p$, one says that $L/K$ is unramified at $\mathfrak P$. If $L/K$ is unramified for all the prime ideals $\mathfrak P$ dividing $\mathfrak p$, one says that $L/K$ is unramified above $\mathfrak p$ (or “at $\mathfrak p$”).