No difference at all, "vanilla js" is just a way to refer to native (standards-based, non-extended) JavaScript. Generally in context it is a term to contrast with using libraries and frameworks (jQuery, React, etc).
Websites like vanilla-js.com play it up as a joke by talking about Vanilla JS as though it was a framework. That does muddy the water a little.
Also it can be a little philosophical given how many things compile to vanilla javascript without being vanilla js themselves.
A simple guideline might be: if you can write the code and run it in any current browser without additional tools or compile steps, it's vanilla js.