What is this mysterious person – an editor – that some people say I need to employ to produce my book?

I get amused when on a forum: Createspace or Amazon, a would be writer asks “Do I need and editor?”
I want to scream – WHAT TYPE OF EDITOR? There are many types, of which the following is only a sample.

Acquisitions Editor
So next time someone says I am an experienced editor, and used to work at “Lick Your Lips” magazine ask: “What type of editor?”