GM (Game Master)

[Enkidoh]

And speaking of FFXI, there was some lore in regards to the Vana'dielian GMs given,(found here), in that they were supposedly a mysterious order of knights who were tasked with specifically policing adventurers - who are, after all, youthful, rebellious, free-spirited, heavily-armed, and can destroy gods:

Little is known about the true origins of the GMs. It is believed they inhabit Atomos, where they hone their skills to use on other Worlds. Some believe they are the heralds of Altana and Promathia, regulating balance over the world and its inhabitants. Others believe they exist to bring misery and anger upon the populace, who often throw curses at GMs due to their absolutism. Though adventurers have slain Vana'diel's mightiest gods, no one has ever defeated a GM, and justifiably so.

Little wonder normal militias/security forces wouldn't be able to deal with them, thus necessitating an independent militia force even more powerful than them. But that was taken from the FFXIcylopedia and their references list SE's own POL website so I'd take that as canon.

It does however ring true, and definitely also fits the Eorzean version. Lacking any other lore about them, explaining the GMs being a police force to oversee adventurers does make sense lore wise, as that's what they do gameplay wise.

As for the GM jail, the FFXI version was called Mordion Gaol, which I believe is also used as the name for the FFXIV version - I remember seeing it being tested out by the development team during the Beta Test and recall the FFXI name being used for it. But as I've never even spoken to a GM in FFXIV, let alone had the dubious honour of experiencing Eorzean tax gil at work first hand I'm not sure exactly.