What about this syntax?

[eluser]jbawarren[/eluser]
So I was looking at the Codeigniter code and ran across an oddly placed ampersand.

In common.php

The function:
function &load;_class($class, $instantiate = TRUE)

The instance:
$error =& load_class('Exceptions');

What exactly does the ampersand do here?

Sorry if it's a beginner question, I'm just curious...and new

Thanks.