Creating Custom Taxonomy without mapping to any post type

It is possible to register a taxonomy without associating a post type by passing null as your argument for the $object_type. Unfortunately, this means that you will still need to associate an object type (post type) to your taxonomy later in order to use it.

register_taxonomy( 'aprwc_rating_criteria', null, $args );

From the documentation:

Setting explicitly to null registers the taxonomy but doesn’t associate it with any objects, so it won’t be directly available within the Admin UI. You will need to manually register it using the ‘taxonomy’ parameter (passed through $args) when registering a custom post_type (see register_post_type()), or using register_taxonomy_for_object_type().