Algebraic Number Theory
《Algebraic Number Theory》 · 第 69 页 · Chapter I，Section 11「Localization」
The valuation associated to $\mathbb Z_{(p)}$, $v_p:\mathbb Q\to\mathbb Z\cup\{\infty\}$, is called the $p$-adic valuation of $\mathbb Q$; if $x=p^\nu a/b$ with $a,b$ relatively prime to $p$, then $v_p(x)=\nu$.