Javascript !function

Question

I use jQuery-UI for an application. This Application uses drag and drop and for mobile support i use jQuery UI Touch Punch.

I was wondering why the function look like this:

!function (a) {
  //code stuff
}(jQuery);

I've never seen an exclamation mark in front of a function.

Here you see the full code: https://github.com/furf/jquery-ui-touch-punch/blob/master/jquery.ui.touch-punch.min.js

What is this good for?