$_FILES

An associative array of items uploaded to the current script via the HTTP POST method.

$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)

Introduced $_FILES that deprecated $HTTP_POST_FILES.

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.

move_uploaded_file() -

Handling File Uploads -