WordPress at a glance
function is not described

the_post_password() WP 2.7.0

Displays the post password.

The password is passed through esc_attr() to ensure that it is safe for placing in an html attribute.

No Hooks.

Return

Nothing (null).

Usage

the_post_password();

Code of the post password: wp-admin/includes/template.php VER 5.0.3

<?php
function the_post_password() {
	$post = get_post();
	if ( isset( $post->post_password ) )
		echo esc_attr( $post->post_password );
}