WordPress at a glance
action is not described

admin_head-media-upload-popup action-hook . WP 2.9.0

Fires when scripts enqueued for the admin header for the legacy (pre-3.5.0) media upload popup are printed.

Usage

add_action( 'admin_head-media-upload-popup', 'action_function_name_834' );
function action_function_name_834(){
	// action...
}

Where the hook is called

wp_iframe()
admin_head-media-upload-popup
wp-admin/includes/media.php 509
do_action( 'admin_head-media-upload-popup' );

Where the hook is used (in WP core)

Does not used.