One is specific, one is general. They're the same role: to adjudicate the rules, arbitrate between players, and facilitate a great experience at the table! “Dungeon Master” is considered “the original” by some; it is the official Dungeons & Dragons term for the role. But there are lots of different games! Dungeons & Dragons is a great sword-and-sorcery adventure game, and it's great for stories like Lord of the Rings or Game of Thrones, but there are games for all sorts of genres. Games for stories like Star Wars and Firefly; games for stories like Indiana Jones and Lara Croft; games for stories like Stranger Things and The Goonies… There are even other games for stories like Lord of the Rings and Game of Thrones! For all of these, the term “Game Master” applies nicely.
The term “Game Master” can also apply to someone leading or teaching other games! For many games, learning from the printed instructions is a confusing slog. With the right teacher, the learning process goes from frustrating to fun! Hiring a GM is a great way to find that teacher when you don't already have one nearby.
“Dungeon Master” is just Dungeons & Dragons's term for “Game Master”. At the end of the day, they're the same thing!
This is a game played by friends, right? The nerdiest one in the group buys the book and invites everyone into a cozy basement for a few hours a week, right?? Well, yes! That's one of the beautiful things about TTRPGs - friends telling stories together! That's why I'm always happy to help other GMs get their start.
But that's the trouble for newbies; without a coach, it can be exceptionally tough to get started. So much institutional knowledge pervades the hobby that even experienced game writers can find it troublesome to convey all that, without overwhelming the reader. It’s like learning to drive: sure, you could learn how to drive by reading a lot about it and then getting behind the wheel… But the learning process is much smoother with an experienced member at the table. Someone who can give pinpoint instruction when the information is relevant, rather than a deluge at the beginning.
There are also benefits for experienced groups! I consider it an honor, a privilege, and a professional development to watch other GMs at work. There are so many ways to give a table a great experience, and I’d be a fool to think I know all of them! There’s also the simple matter of fatigue. Some GMs want to play, too! Your home GM deserves to kick back and play their own character sometimes. Trust me, they can get tired.
Trust falls and guessing games get stale quick. Do you want your team working together on problems, getting to know one another better, and feeling a true rush of adventure? Hire a Game Master. The right GM can work with teams of all sizes; streamlining and subcontracting for larger groups, focusing on precision and personalization with smaller groups. A sense of individual agency plied toward shared purpose is the bread and butter of a freelance GM - and isn't that the mindset you hope to achieve? Hire a freelance GM. Step away from the desk, pick up your sword, and hold the line!