Template Variables
From Documentation
Template variables are special formated text that when ran through the browser fills it with the desired text. For example if you open the template file layout.tpl.php in the title you will see:
<title>{$title}</title>
The portion {$title} is a template variable and used to display the title of your site. The layout file includes variables that are available through out your site. But each internal page can have different variables depending on the page.