What is the fn in the snippet
<p>I am looking at the jquery watermark plugin and i cant seem to understand whats going on... First off what does the fn mean and where is WatermarkColor being defined...ins not in this file</p>

<pre><code>$.fn.Watermark = function(text,color) {
    if(!color)
        color="#2D2D2D";
    return this.each(
        function(){     
            var input=$(this);
            var defaultColor=input.css("color");
            map[map.length]={text:text,obj:input,DefaultColor:defaultColor,WatermarkColor:color};
            function clearMessage(){
                if(input.val()==text)
                    input.val("");
                input.css("color",defaultColor);
            }
</code></pre>
