[WordPress] What Are WordPress User Caches?

00-get-user-login.php

<?php
$user = get_user_by( 'login', $username );

01-get-user-email.php

<?php
$user = get_user_by( 'email', $email );

02-authenticate-user.php

<?php

// Clean out any cookies and cookies for an existing user.
clean_user_cache( $user->ID );
wp_clear_auth_cookie();

// Set the current user and update the caches.
wp_set_current_user( $user->ID );
wp_set_auth_cookie( $user->ID, true, false );
update_user_caches( $user );