WordPress at a glance
action is not described

install_plugins_upload action-hook . WP 1.0

This action is documented in wp-admin/plugin-install.php

Usage

add_action( 'install_plugins_upload', 'action_function_name_6607' );
function action_function_name_6607(){
	// action...
}

Где вызывается хук

В файле: /wp-admin/plugin-install.php
install_plugins_upload
wp-admin/plugin-install.php 156
do_action( 'install_plugins_upload' );

Где используется хук в ядре WordPress

wp-admin/includes/admin-filters.php 83
add_action( 'install_plugins_upload', 'install_plugins_upload' );