Latin, short for the quo peregrinatur grex, pastor secum: "wherever the flock wanders, so does the shepherd". In Walter M. Miller, Jr.'s post-apocalyptic masterpiece A Canticle for Leibowitz, this is the code name for the Catholic Church's contingency plan for preserving the apostolic succession in the event of global thermonuclear war. The idea is to send a spaceship full of priests and a bishop or two out to a remote colony (the nations of Earth having developed genuine space travel before ubiquitous universal annihilation technology this time around), there to abide indefinitely (space travel remaining slower than light) and form a new branch of the church. The head bishop of the colony then gets to be the Pope in a sort of peaceful schism, since he is obliged to act as though the Church on Earth did not exist.

Aside from the entertaining exploration of the boundary conditions of the structure and rules of the Catholic Church, this is a proclamation of Miller's hope for mankind: even though we sin in the same ways and suffer the same consequences again and again, we always manage to stay one step ahead of the Devil and live to try again. (It would be cynical to taint this message of eternal hope by pointing out that Miller committed suicide while working on the sequel to this book and is therefore himself damned for all eternity in the eyes of the Church, so I won't.)