<p>Module positions are placeholders in a template. They identify positions within the template and tell the Joomla! application where to place output from modules assigned to a particular position. The template designer has complete control over module positions, creating variations between templates and the respective Joomla! default positions assigned to modules in the installation sample data.
</p>
<p>
For example, the module position Left could be defined to be on the left side of the template to display a site navigation menu. So if a module is assigned the Left position, it will be displayed wherever the designer puts that Left module position - not necessarily the left side of the page.</p>

<p><strong>Reference: <a  href="http://docs.joomla.org/Glossary" 
        title="read the reference" 
        alt="read the reference" 
        target="_blank"
        rel="nofollow">http://docs.joomla.org/Glossary</a>
</strong></p>
