What does __FILE__ mean?

Question

I have the following code from Codeigniter index.php

My understanding is that,

If / of string position in $system_folder

Answer 1

__FILE__ is simply the name of the current file. realpath(dirname(__FILE__)) gets the name of the directory that the file is in -- in essence, the directory that the app is installed in. And @ is PHP's extremely silly way of suppressing errors.