What are the best practices for storing variables in PHP to ensure they are retained even after closing the browser?

To ensure that variables are retained even after closing the browser in PHP, you can use sessions to store the variables on the server-side. By using sessions, the variables will be available across different pages and even after the browser is closed. You can start a session at the beginning of your PHP script and store the variables in the $_SESSION superglobal array.

<?php
session_start();
$_SESSION['variable_name'] = 'value';
?>