The meaning of Fair in D&D -but more on topic this time

Alright

So we know how the last one went, but I do feel like this is an interesting question to answer. So here's my take:

"Fair" in D&D is something with many meanings, but I think it kinda boils down to "The DM is a "fair" DM if they effectively communicate with the players, and are adaptable enough to change parts of the campaign if it makes some of the players uncomfortable or otherwise unhappy. Because in the end, D&D is a partnership game- the DM agrees to provide a fun experience for everyone, and in turn, the players agree to cooperate with what the setting or campaign is and not be ridiculous about it.

TL:DR A fair DM is a DM who communicates with the players and can adapt the campaign to help everyone have fun and be comfortable.

Thoughts?

Well, the prior discussion heavily mixed 'fair' and 'good', and I think your choice does as well.

Fair does not have any particularly D&D specific meaning, so we can just use a dictionary definition of fair. Particularly appropriate definitions are

a(1) : marked by impartiality and honesty : free from self-interest, prejudice, or favoritism

b(1) : conforming with the established rules : allowed

I would say it's very hard to be a good DM without also being fair per a(1), but being fair per b(1) is optional.

I'd say fair as per b(1) works fine in, say, a board game, where the rules lay out a clearly defined full game, hundreds of contingencies, etc., but not so much in D&D, where the rules are more "Here's magic powers, here's how the system works, and here's how stuff you'll need works. Now go have fun!", and a DM can kinda just put a Tarrasque in front of a level one party for no reason. Is that fair by b(1)? Yes, because the rules say you can. Is that fair by... well, an emotional metric? absolutely not. Now, I am not emotionally intelligent enough to tell you WHY it's unfair, the best I could manage is "because it is not fun", which is faulty by many metrics, but I think we can all agree that it isn't fair. Now, this goes both ways, as for example Silvery Barbs is often rated by DMs as "unfair" and therefore banned because it can result in turning any fight into a cakewalk, which does not tend to come off as "fair".

But I agree, it's very hard, if not impossible, to be a good DM without being A(1) fair, and sometimes to be A(1) fair you have to house rule or homebrew, which breaks b(1)'s definition of Fair

Fair (a) is important, although it doesn't require treating everybody anything close to equally, since not everybody wants the same thing out of the game.

Fair (b) is about the rules of the social contract, not the game mechanics. (Although level of adherence to the mechanics is part of the social contract.) But a lot of the rules of the social contract are unwritten, and that's going to be true even of you have an explicit session zero. "The DM is not going to arbitrarily kill the PCs" is up there along with "the players are going to engage with the game the DM is running".

(And, (a) is really subsumed by the social contract as well.)

If we put aside "good", which to me involves a lot more ensuring all the players are having fun. IMO a fair DM has the following requirements:

1) Making consistent and predictable rulings. This might be consistent with the published rules, or with their homebrew system. 

2) Narrative events and NPC reactions should be consistent with the tone, setting, and themes of the game. A comical surrealist campaign might have the players suddenly fall through a puddle into a land of lollipops and chocolate fairiess, but not a gritty realistic campaign.

3) Not force the player characters into a situation where they will almost certainly die. There should always be a way out, or the players should have made a well informed choice to enter the situation. 

4) Not engineer every situation so that the player characters always win. - For a game to be fair there must be a possibility of failure.

 I think the players and the DM construct whatt fair means at their table. This can be done in an intentional way by starting with clearly communicated expectations and boundaries in session zero and continuing to communicate when things happen and those expectations and boundaries need to be revisited (or reminders need to be made). Or this can be done unintentionally by a group of players and a DM dealing with things in a straightforward, tactful manner as they come up. Both rely on communication, just one front-loads it and the other has it happen on the fly. Either way, it's the players and the DM participating in the social contract with each other and collaborating to build group cultural norms at their table. Consistently following the established norms is fair. Failing to do that is where people start feeling fairness isn't being respected.