1. I am utilizing a WordPress site.
  2. I am including this script within the header.

Once the script loads, I recieve this error:

TypeError: 'undefined' is not a function (evaluating '$(document)')

I've no clue what's leading to it or what it really even means.

In firebug, I recieve this: $ is not a function

The apparent answer. Have you range from the jquery.js? I'd exactly the same kind of error when utilizing LightBox. I didn't remember to incorporate the LightBox.js. How silly :D

Wordpress uses jQuery in noConflict mode automatically. You have to reference it using jQuery because the variable title, not $.

It is simple to wrap this up inside a self performing function to ensure that $ describes jQuery again (and eliminates polluting the worldwide namespace too), e.g.

(function ($) {
   $(document);
}(jQuery));