WordPress at a glance
action is not described

validate_password_reset action-hook . WP 3.5.0

Fires before the password reset procedure is validated.

Usage

add_action( 'validate_password_reset', 'action_function_name_9450', 10, 2 );
function action_function_name_9450( $errors, $user ){
	// action...
}
$errors(object)
WP Error object.
$user(WP_User/WP_Error)
WP_User object if the login and reset key match. WP_Error object otherwise.

Where the hook is called

In file: /wp-login.php
validate_password_reset
wp-login.php 655
do_action( 'validate_password_reset', $errors, $user );
woocommerce/includes/class-wc-form-handler.php 1039
do_action( 'validate_password_reset', $errors, $user );

Where the hook is used (in WP core)

Does not used.