(PHP 4 >= 4.1.0, PHP 5, PHP 7)
$_FILES -- $HTTP_POST_FILES [deprecated] — HTTP File Upload variables
An associative array of items uploaded to the current script via the HTTP POST method. The structure of this array is outlined in the POST method uploads section.
$HTTP_POST_FILES contains the same initial information, but is not a superglobal. (Note that $HTTP_POST_FILES and $_FILES are different variables and that PHP handles them as such)
Note:
This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods.