wp_ajax_nopriv_(action) action-hook . WP 2.8.0

Fires non-authenticated Ajax actions for logged-out users.

The dynamic portion of the hook name, $action, refers to the name of the Ajax action callback being fired.

Usage

add_action( 'wp_ajax_nopriv_(action)', 'action_function_name_6025' );
function action_function_name_6025(){
	// action...
}

Where the hook is called

do_action( "wp_ajax_nopriv_{$action}" );

Where the hook is used (in WP core)

add_action( 'wp_ajax_nopriv_heartbeat', 'wp_ajax_nopriv_heartbeat', 1 );