What is the $current_screen global variable?

What does it mean by a screen? I’ve had a look in the codex and don’t understand (I’m a newbie). Thanks.

$current_screen is a global variable in admin screens. It holds the result of WP_Screen::get( $hook_name )->set_current_screen();.

WP_Screen is a class, get() is a static method that returns a real object – an instance of WP_Screen with some predefined properties:

$screen->base       = $base;
$screen->action     = $action;
$screen->post_type  = (string) $post_type;
$screen->taxonomy   = (string) $taxonomy;
$screen->is_user    = ( 'user' == $in_admin );
$screen->is_network = ( 'network' == $in_admin );
$screen->in_admin   = $in_admin;

$hook_name is a page specific variable for different admin pages.

set_current_screen() pushes the object properties into the global variable. I consider this as a rather poor step. It is done for backwards compatibility, I guess.

You can use $current_screen on plugin pages, in metaboxes and other places to get some context information.

Example:

if ( $GLOBALS['current_screen']->is_network and is_super_admin() )
{
    // do something specific for network admins
}