It is an iframe.
You DO NOT need to use iframes. They are not the best tool to use, especially when it is so easy to change content.
Have you heard of PHP includes???
They are great, and save a hell of a lot of time.
Say if the code is exactly the same on all of your pages, and the only thing that changes is the centre content, you can put all of the code in one file, and just use the php include to include it into the webpage. Below is what one of my pages looks like as raw PHP.

PHP: Select all

 
<?php include ('includes/header.php'); ?>
 
<div id="contentleft">
<?php include ('includes/navigation.php'); ?>
</div>
<div id="contentcenter">
 
CONTENT GOES HERE
 
</div>
<?php include ('includes/footer.php'); ?>

As you can see on this particular page I have 3 files that I call from the server. The Header and Footer are EXACTLY the same throughout my site since I include these. Therefore if i needed to change something at the bottom of a page I would not need to change EVERY SINGLE page, just ONE file. This saves a lot of time and also means you can put your content in one place without messing up your tables etc.
I hope you find this useful and use this. I started off coding each page, and when I needed to change something i would spend ages going through each file repeatedly.

Craig