init
init is an action that is fired after everything in WP has been loaded, but before wp() has been run.
Context:
File: wp-settings.php
function shutdown_action_hook() {
do_action('shutdown');
wp_cron();
wp_cache_close();
}
register_shutdown_function('shutdown_action_hook');
// Everything is loaded and initialized.
do_action('init');
This hook provides no parameters. You use this hook by having your function echo output to the browser, or by having it perform background tasks. Your functions shouldn't return, and shouldn't take any parameters
This hook is an action which means that it primarily acts as an event trigger, instead of a content filter. This is a semantic difference, but it will help you to remember what this hook does if you use it like this: add_action('init', 'your_function');