WordPress at a glance
filter is not described

admin_url filter-hook . WP 2.8.0

Filters the admin area URL.

Usage

add_filter( 'admin_url', 'filter_function_name_3548', 10, 3 );
function filter_function_name_3548( $url, $path, $blog_id ){
	// filter...

	return $url;
}
$url(string)
The complete admin area URL including scheme and path.
$path(string)
Path relative to the admin area URL. Blank string if no path is specified.
$blog_id(int/null)
Site ID, or null for the current site.

Where the hook is called

get_admin_url()
admin_url
wp-includes/link-template.php 3080
return apply_filters( 'admin_url', $url, $path, $blog_id );

Where the hook is used (in WP core)

Does not used.