Action Hook
A WordPress function that lets you execute custom code at specific points in the WordPress loading process without modifying core files.
An action hook in WordPress is a predefined point in the WordPress execution cycle where you can attach your own custom functions. WordPress fires hundreds of action hooks during a page load, from initialisation (init) to rendering the header (wp_head) and footer (wp_footer).
You attach a function to an action hook using add_action(). This is the foundation of WordPress plugin and theme development, as it allows you to extend WordPress behaviour without editing core files. Filter hooks are the equivalent mechanism for modifying data rather than triggering actions.