Sinal de cifrão ($) no javascript

Eis um bloco de código em java script:

Object.extend(Element, { visible: function(element) {	return $(element).style.display != 'none'; }, toggle: function() {	for (var i = 0; i < arguments.length; i++) { var element = $(arguments[i]); Element[Element.visible(element) ? 'hide' : 'show'](element);	} }, hide: function() {	for (var i = 0; i < arguments.length; i++) { var element = $(arguments[i]); element.style.display = 'none';	} }, show: function() {	for (var i = 0; i < arguments.length; i++) { var element = $(arguments[i]); element.style.display = '';	} }, remove: function(element) {	element = $(element);	element.parentNode.removeChild(element); }, update: function(element, html) {	$(element).innerHTML = html.stripScripts();	setTimeout(function() {html.evalScripts()}, 10); }, getHeight: function(element) {	element = $(element);	return element.offsetHeight; }Alguém sabe me dizer pra que serve o sinal **$** no javascript? 

Valeuu!!