What is the difference between $ (document.body) and this $ ("body") in jquery?

Both ways represent the same object
$ ("body") is a selector, and JQuery starts searching from the top of the DOM until it finds an element labeled body.
While the Document.body in $ (document.body) is already a DOM object, jQuery can use this element directly.
So the difference between them is efficiency, $ (document.body) above $ ("body")
But generally in the ordinary single page is not reflected.

What is the difference between $ (document.body) and this $ ("body") in jquery?