While I explore this site, I occasionally see the phrase "GM fiat" (or "DM fiat", for D&D questions and answers), but I don't know the exact meaning of that. I want to know the meaning of that terminology.
Terminology – What is GM/DM Fiat?
terminology
Related Solutions
Minimization and Maximization for Optimization
Min-max (minmax) comes from using mathematics to solve optimization problems. An example is finding the maximum area for a given perimeter.
- As applied to RPG's (the example will be D&D 5e) min-max addresses how to best assign ability points, equipment, and skills to get the most power or effectiveness within the game as reflected in the game's mechanics.
The player accepts penalties in areas that hamper his character's in game effectiveness least.
- The player makes tool and equipment choices that give the most benefit as measured by the game's mechanics.
Example: The Fighter chooses the most possible Strength and Constitution, and accepts that his Intelligence or Wisdom scores will be suboptimal.
The point buy system (you don't get to start with all 18's) in Basic Rules, page 8, is a good illustration of this. It shows the difference between the min/max 27 point buy of 15/15/15/8/8/8 versus the "median" approach of 13/13/13/12/12/12.
- The former has a number of +2 bonuses, and some -1 penalties, whereas the latter has a collection of +1 bonuses.
- When the character then applies racial bonuses, some of those values with increase to +3 in the former, and +2 in the latter).
- An analogue from regular life: budget your monthly paycheck/income. Depending on what your needs, desires or goals are, you spend money where you wish to maximize a goal (such as a either the nicer car or the nicer apartment) and accept a sacrifice in another area (the not as nice apartment or car) so that you get the most out of the limited dollars you have in your budget based on what is most important to you. (In this example, assume that you are buying a car with a loan that has a monthly payment).
Thanks to Lucas' suggestion to amplify ...
In systems where characters can add to their base abilities as levels progress, the decision to keep "pumping" a given score, be it Strength, Intelligence, etc, toward it's maximum permissible value to accrue more bonus points (additions to die rolls or ability to set higher DC's for spells) is a form of optimization. If you apply this to the 15 15 15 8 8 8 example above, the player would keep boosting Strength to 17 or 18 or 20 while still not improving upon the sub optimal scores. While this may help the party, in their need for the best fighter they can hope to have by their side, it is a form of optimization in the min/max style.
If the minmax approach is taken as an end in and of itself by one player in a group, it can cause conflict at the gaming table. The GNS theory (Gamist, Narrativist, Simulationist) and the experience of many RPG players suggest that focusing exclusively on mechanics driven optimization is incompatible with the other core elements of role playing.
Full Disclosure: Since 1e, I most often boost Dexterity on any character since it has an impact on initiative, armor class, dodging, and missile weapon use. While an agile cleric or wizard may or may not make sense, I assess the game's system and try to give my player the better chance to act before the monsters, or to not be hit. This is a deliberate choice. It is informed somewhat by books, cartoons, movies and other stories where the main character is just missed by that arrow, narrowly dodges a blow, ducks under the swinging cleaver, barely gets under the closing door/gate that is descending, just catches the swinging vine, etc. In RPG's, the characters are the heroes of the story as it comes to life during the serial sessions of play.
@Trinidad's point on possible confusion in terms is worth adding as a footnote. *In mathematics there are at least two uses of the term: one is regarding to linear programming that may apply to RPG's usage, while the other is related to decision theory that is most applicable to multiplayer game strategy.
Resistance is a perfectly fine word by itself, so long as you do not end up with other types of resistance (energy resistance, for instance).
Willpower would work if your magic is primarily mental, though it's not ideal when better willpower helps you resist explosions.
Warding/Wards would work. It implies a physical object doing the protecting, but then so does Armor.
Best Answer
In a large number of RPGs the GM is positioned as the controller of the world, its NPC inhabitants, the items in the world, and their essential natures. They are also often positioned as the final arbiter of rules and thus hold considerable authority. It tends to be these games in which “GM fiat” is a thing. Hopefully a GM imbued with such power will remember: with great power comes great responsibility.
With that said, a fiat is defined as:
So a GM fiat is when the GM says something is the case—because the game or environment gives the GM authority to do this—and simply by doing so it becomes the case.
A GM fiat is produced independently by the GM. It is separate to decisions made by the group as a whole: a GM can declare a house rule as a GM fiat, but that's different to the group producing a house rule together. Implicitly the GM is not generally expected to have to justify or explain their fiat; they can simply decree it and it is so.
Because GM fiats are arbitrary and can involve major changes (like the changing of the rules themselves) the motto of “with great power comes great responsibility” is massively relevant. These changes could make the game more fun or extremely un-fun for players. Sometimes GM fiat gets wielded like a hammer so that whatever the GM wants, happens. Our hobby is fundamentally about people having a conversation for a while to collaborate and create fun for themselves and each other; many changes that materially affect players outside the course of simply running the game world will be better handled by discussion, buy-in, and consent rather than fiat.
Some examples of usage of GM fiat