The phrase “Dungeon Master” is a registered trademark[1] by the rights holders of Dungeons and Dragons. DM is the abbreviation of that, and most likely safe to use.
Game Master (GM) is used as a generic (and game agnostic) term.
Edit:
I have (twice) edited this now after additional information from others (thank you Kichae for the link to the Dungeon Master trademark) was posted on this thread.
I don’t think DM is a trademark, but if you have other information feel free to provide it. Looking through older discussion forums on this topic, the only semi-definitive answer I’ve found is in this 2021 thread where somebody referred to a now-defunct US gov’t trademark search link, where they said they found a lot of "DM"s registered but none related to D&D. I’m inclined to believe it was a working link at that time and they weren’t just making shit up.
Personally I use the term DM because I’ve mostly played D&D, so to me it’s more natural.
The phrase “Dungeon Master” is a registered trademark[1] by the rights holders of Dungeons and Dragons. DM is the abbreviation of that, and most likely safe to use. Game Master (GM) is used as a generic (and game agnostic) term.
[1] https://trademarks.justia.com/742/64/dungeon-74264094.html
Edit: I have (twice) edited this now after additional information from others (thank you Kichae for the link to the Dungeon Master trademark) was posted on this thread.
I don’t think DM is a trademark, but if you have other information feel free to provide it. Looking through older discussion forums on this topic, the only semi-definitive answer I’ve found is in this 2021 thread where somebody referred to a now-defunct US gov’t trademark search link, where they said they found a lot of "DM"s registered but none related to D&D. I’m inclined to believe it was a working link at that time and they weren’t just making shit up.
Personally I use the term DM because I’ve mostly played D&D, so to me it’s more natural.
“DM” is not a trademarked term, because it’s a pair of letters. “Dungeon Master” is absolutely a trademarked term, though, and has been since the TSR days.
Thank you for this information, I have added it to my original comment.