How does WordPress core architecture and plugin system work?

WordPress core architecture is built on PHP and MySQL, with a plugin system that allows developers to extend functionality through Hooks mechanism. WordPress provides two main hook types: Actions and Filters. Action hooks are used to execute custom code at specific points in time, while filter hooks are used to modify data. Developers can register hooks using add_action() and add_filter() functions, and trigger hooks using do_action() and apply_filters(). Theme development follows a template hierarchy including header.php, footer.php, index.php, single.php, page.php and other template files. WordPress also provides rich APIs such as WP_Query for querying posts, WP_User for user management, WP_Post for post object manipulation, etc. Additionally, WordPress REST API allows developers to create custom endpoints for headless development.