What is VBO Total in the Stats window?

I read what the manual says. I still don't understand it, because in a scene with 4 visible objects with mesh renderers, VBO total is anywhere from 25 to 37. If I turn on static batching, the draw calls drop from 4 to 1 but the VBO is unaffected.

So what is this number really measuring, and what is a safe value to keep it under to target current generation iOS devices? ( I realize that is a separate question, but it's my reason for asking the first question, so is relevant. )