The answer to this question could be trivial !
According to the wikipedia page:
A perfect elimination ordering in a graph is an ordering of the vertices of the graph such that, for each vertex $v$, $v$ and the neighbors of $v$ that occur after $v$ in the order form a clique.
I'm not sure if I understand completely the definition .
Could somebody explain a little bit the definition, or give some example to illustrate the idea ? ( I have not understand the following sentence "that occur after $v$ in the order")
Any idea will be useful!