Session Library — CodeIgniter 4.1.4 documentation
What is Session Data? ¶ Session data is simply an array associated with a particular session ID (cookie). If you've used sessions in PHP before, you should be familiar with PHP's $_SESSION superglobal (if not, please read the content on that link). CodeIgniter gives access to its session data through the same means, as it uses the session handlers' mechanism provided by PHP.