Something broadly similar to the 'Status', 'Priority', and 'Category', select lists in the Drupal issue tracking system (example).
Schema.org has the rather unsatisfactory actionStatus property, with a measly four ActionStatusType values to pick from. I can get around that by categorising each of our longer list of values as one of those four (or none, if necessary). That's actually a good general solution for extending the spec.
So actionStatus is a select list which applies to entities (terms) in that bundle (vocabulary).