What is $ in function($) mean???

What is $ in function($) mean???

I am very new to jquery-ui and am trying to follow the examples in the book Jquery UI 1.8 The User Interface Library for Jquery.


I don't understand the $ and jquery as in:

<script>

      (function($) {                            // the $ ?
            $("#myDialog").dialog();
      }) jquery;                                  // jquery ?

</script}

nor what the ()'s surrounding the function are supposed to do.

I removed  the $ and Jquery and the code doesn't work.

Thanks for any help in explaining this.

R