Codeigniter 4 is MVC framework, MVC refers to Model, View and Controller. Here controller is used to backend, model is used to manage tables (database). And view used to user interface.
CodeIgniter is an open-source software rapid development web framework, for use in building dynamic web sites with PHP. CodeIgniter is a PHP MVC framework used for developing web applications rapidly. CodeIgniter provides out of the box libraries for connecting to the database and performing various operations like sending emails, uploading files, managing sessions, etc.