While you work hard to make sure that every link actually goes to a specific web page on your site, there is always a chance that a link clicked will slam dunk and become a famous 404 ERROR PAGE NOT FOUND.
404.php
<!DOCTYPE html>
<html>
<head>
<title>404 Page</title>
</head>
<body>
<?php get_header(); ?>
<br/>
<h1 style="color:yellow">404 Page</h1>
<?php get_footer(); ?>
</body>
</html>
