Forse è più comprensibile se ti metto tutto il codice:

<!--
You are free to copy and use this sample in accordance with the terms of the
Apache license (http://www.apache.org/licenses/LICENSE-2.0.html)
-->

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:v="urn:schemas-microsoft-com:vml">
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8"/>
<title>Google Maps V3 API Sample</title>
<script type="text/javascript" src="http://maps.google.com/maps?file=api&amp;v=2.x&amp;key=ABQIAAAAddD3O5fXuL _HtKIUrjJ-ahSuL8FB-3nxjrLtXKyxIpjPm1Kp3xRvHfX4ZC0GDp_MreM6ZsPf6aHz9w" ></script>
<script language= "Javascript">

var map = null;
var geocoder = null;
var Lat = null;
var Lon = null;

function createMarker(point, description)
{
var marker = new GMarker(point);
GEvent.addListener(marker, "click", function ()
{
marker.openInfoWindowHtml(description);