According to Christus Dominus 18, it is “migrants, exiles and refugees, seafarers, air-travelers, gypsies, and others of this kind. Suitable pastoral methods should also be promoted to sustain the spiritual life of those who go to other lands for a time for the sake of recreation.”
I had to smile at the latter, thinking of a few bishops who promote vacation packages or cruises. Somehow, that wasn’t quite what CD 18 had in mind.
But seriously, episcopal concern for the spiritual welfare of these people, some of whom are not the most popular folks in your average parish, would need to be assisted by the lay apostolate. Not every wanderer is served by a bishop hosting a pleasure cruise. What if bishops were to lead delegations to migrant camps? What if they travelled off the familiar Alaskan or Caribbean cruise routes?