Let $\displaystyle R$ be a relation on $\displaystyle \mathbb{Z}$, where $\displaystyle xRy \Leftrightarrow x|9y$. State whether R is reflexive, symmetric, transitive or an equivalence relation.

I'm having trouble understand the notation | in the question. I am used to this meaning "such that". The text doesn't explain this problem very well; it says that x must = 9ky were $\displaystyle k \in \mathbb{Z}$

How do I go about determining the relation here?

Thanks.