$ at the beginning and at the end of variable

Possible Duplicate:
Why would a JavaScript variable start with a dollar sign?

I realized some syntax with jquery and didnt know what it is. here goes:

var $foo = $("bar").blah();

var hello$ = $("stgelse").etc();

What is the difference between these? and why are they like that?

Also, For example:

var $foo = $("").blah();

var should already contain whatever right side is returning ? no?

Can you please elaborate?