It means that when something is not standing steadily, and it can fall down, or wobble over.
For example: A baby can wobble over when sitting. A vase can wobble over. A stuffed animal with a big head can wobble over because its big head is pulling the whole thing down.
The pile of bricks wobbled, then fell.
My baby is trying to sit on her own but yesterday she always wobbles over. It is very funny :)
I hope I could help.