Around the site there are many things that are abbreviated examples are:
Are these ok to use? The first example is one that is used everywhere and I therefor assume it is but the second one isn't (to my knowledge) used by the Dev team of dnd 5e.
Simply put what abbreviations are ok?
Being an abbreviation isn’t relevant: the measure we care about is whether the words used make the post clear. It’s especially important in questions: clarity is so major a measure that not enough clarity is a standard hold reason.
So in general, just consider whether most RPG.se readers will know what an abbreviation means without having to google it. If most wouldn’t know it, it needs to be spelled out fully. (If it’s a long phrase that’s repeated often in the post, best writing practices are to spell it out in full the first time the abbreviation appears, like “Leomund’s Tiny Hut (LTH)”, so that later the abbreviation can be read unambiguously.)
Incidentally, I see no problem with the way the linked question is written. It’s uses the full name first, and since the post is short it’s clear what “LTH” means when it appears.
* Aside, none of “DnD”, “dnd”, “Dnd”, “D&d”, or “d&d” follow the rules for how abbreviations are formed in English. If I’m improving a post for other reasons, I will fix those to the correct “D&D” just like any other spelling and grammar fixes the post needs. (“D’n’D” is also a correct English formation, but nobody uses that for Dungeons & Dragons.) The only reason our tag isn’t D&D-5e is because & and capitals are forbidden in tag names for technical reasons.
For common abbreviations, like "D&D", everyone knows what you're talking about. However other, lesser known ones can lead to confusion.
Sometimes you can take it from context, but the best option is to lead with the full phrase, followed by the abbreviation, to clarify.
Leomund's Tiny Hut (LTH)
This way it is clear what you're referring to.
As for knowing what requires the abbreviation - common phrases like D&D, AC, DC, CR are usually fine, as they are common abbreviations that everyone use. However things like spells or abilities are a bit more "niche". Therefore abbreviating those are more of a cop-out, rather than having to type the whole phrase everytime.
First off, in writing a post you're trying to communicate to an audience. Or to audiences. As a question writer your audience is "the universe of people who might see this and give me a helpful answer." As an answer writer your audience is "the querent." But it's also often "the long tail of visitors and readers who will ever see this post." (See We're working on a new stat... esp. at "You've got to get this to get us.")
What abbreviations to use, then? Well, it depends on your audience. If you're writing a question and want to use commonly-used abbreviations in your game, go for it. Remember that you may end up limiting those who feel drawn to answer the question the more you use jargon: that may be a desired outcome, depending on your use-case, or it might be a detriment. Your call.
If you're writing an answer I'd say it's completely reasonable to use any abbreviations used in the question. Not only is the querent familiar with them, but it's fair to assume that future readers of your answer have also read the question. (And if not I'm less worried about their opinion.)
Part of making this the greatest repository of RPG-related Q&A the world's ever seen is making sure it gets seen! To that end discoverability is important for posts, too. I have a hard time imagining, for instance, the abbreviation LTH (used exclusively) helping a post get seen by someone searching the site or the internet for Leomund's tiny hut. If the hut's going to be mentioned thirty times feel free to abbreviate it twenty-nine of those times. But write it out the first time.
D&D/DnD/&c., on the other hand, are explicitly part of how our site organizes itself: look at our tags, after all! Abbreviations like AC, HP, DnD,... being ubiquitous through posts and site mechanics makes these pretty safe for discoverability. Your SP may not be another's SP, though, so that one's worth spelling out once or twice. THHGTTGTTRPG? Your guess is as good as mine =)
