At times, people may visit your site via someone else's site who is "framing" your site.  That is they are putting your content into a frame of their window which can appear to be part of your site but is not.  Other times, you may have a need to make sure your page is viewed as the only frame in the browser.  In either case, a simple javascript solution is to add:

<script language="javascript" type="text/javascript">

if (top.location != self.location)
{
    top.location = self.location;  
}

</script>

Or:

<script language="javascript" type="text/javascript">

if (top.frames.length!=0)
{
    top.location=self.document.location;
}

</script>