abstract algebra – Associated Prime notation

Let $I$ be an ideal of ring $R$ with $Ineq R$. Prime ideal $P$ of $R$ is said to be an associated prime of $I$ in the sense of Bourbaki, if $P=(I :_R x)$ for some $xin R$. In this case we say that $P$ is a $ B$-prime of $I$.

Can anyone explain meaning of notation $(I :_R x)$?