Some of the commonly used wordpress path references:
// gives you the url of your theme dir. works for childtheme. get_stylesheet_directory_uri() // get child stylesheet get_stylesheet_uri() // gives you the root theme folder, ie xxx/wp-content/themes get_theme_root() // this gives you the absolute path get_template_directory(); // gives you the plugin url plugins_url(); // gives you the plugin dir path plugin_dir_path(); // ABSPATH refers to the directory in which wordpress is installed, for eg /var/www/htdocs/wordpress ABSPATH // Absolute path to plugins dir WP_PLUGIN_DIR // Absolute path to plugin URL WP_PLUGIN_URL // gives your the url of the homepage site_url()
another good resource is http://codex.wordpress.org/Determining_Plugin_and_Content_Directories
