WordPress at a glance
action is not described

wp_insert_site action-hook . WP 5.1.0

Fires once a site has been inserted into the database.

Usage

add_action( 'wp_insert_site', 'action_function_name_1304' );
function action_function_name_1304( $new_site ){
	// action...
}
$new_site(WP_Site)
New site object.

Where the hook is called

wp_insert_site()
wp_insert_site
wp-includes/ms-site.php 87
do_action( 'wp_insert_site', $new_site );

Where the hook is used (in WP core)

wp-includes/ms-default-filters.php 44
add_action( 'wp_insert_site', 'wp_maybe_update_network_site_counts_on_update', 10, 1 );
wp-includes/ms-default-filters.php 47
add_action( 'wp_insert_site', 'wp_maybe_transition_site_statuses_on_update', 10, 1 );