What does $|V|=O(|E|)$ mean?

I was reading about Dijkstra’s algorithm from this Stanford University lecture presentation. On page 18 it says Dijkstra’s algorithm is $ O(|V|\log|V|+|E|\log|V|)$ and I understand why. But then it says that $ O(|V|\log|V|+|E|\log|V|) = O(|E|\log|V|)$ , because $ |V|=O(|E|)$ . What does $ |V|=O(|E|)$ mean and why is it so?