When you need more than just ‘categories’ and ‘tags’ use custom taxonomies.
Especially useful in combination with custom post types.
add_action('init', 'my_new_taxonomies');
function my_new_taxonomies() {
$labels = array(
'name' => __( 'Action Hooks' ),
'singular_name' => __( 'Action Hook' ),
'search_items' => __( 'Search Action Hooks' ),
'popular_items' => __( 'Popular Action Hooks' ),
'all_items' => __( 'All Action Hooks' ),
'parent_item' => null,
'parent_item_colon' => null,
'edit_item' => __( 'Edit Action Hook' ),
'update_item' => __( 'Update Action Hook' ),
'add_new_item' => __( 'Add New Action Hook' ),
'new_item_name' => __( 'New Action Hook' ),
'separate_items_with_commas' => __( 'Separate hooks with commas' ),
'add_or_remove_items' => __( 'Add or remove hooks' ),
'choose_from_most_used' => __( 'Choose from the most used hooks' ),
'menu_name' => __( 'Action Hooks' ),
);
register_taxonomy('action_hook','post',array(
'hierarchical' => false,
'labels' => $labels,
'show_ui' => true,
'query_var' => true,
'rewrite' => array( 'slug' => 'action_hook' ),
));
}