To get an idea of what people think Truth means, and for reference, I'll write a separate answer giving snippets.
Islam.SE
These questions are basically examples of what C.SE calls "Truth Questions"; questions not about studying the topic of the religion, rather they're trying to find out and/or prove which interpretation/denomination is "more correct." -- goldPseudo ♦, 2014
I have seen comments, edits, questions and even tags posted for pretty much the sole purpose of pushing a particular Truth. -- goldPseudo ♦, 2015
If I had to pick any one trait to watch out for, it's that aggressive apologetic is concerned almost exclusively with promoting ones own viewpoint rather than with anything the questioner actually cares about. This is exactly the opposite of what needs to happen on a Stack Exchange site focussed on high-quality questions and answers. -- goldPseudo ♦, 2017
Christianity.SE
Christianity.SE meta has a "truth-questions" tag.
Tour page and On Topic page:
"Truth" questions that do not focus on what a specific group of people teaches
Close reason:
Questions asking for the truth or validity of a particular doctrine or belief (aka Truth Questions), and questions asking Is X a Sin? are not a good fit for our site, due to their subjective nature, and the vast number of possible Christian opinions on such topics. See: We can't handle the truth -- close reason
We can't handle the truth, 2014
First understand that a "Truth Question" asks what is true. A "Christianity Question," as deemed appropriate for our site, can ask what Christians believe or do. And more specifically, it asks what a specific group or subset of Christians do. -- Flimzy
Truth Question- What is truth?, 2015
Lee Woofenden:
What is the truth is a matter of opinion, and there are almost as many opinions as there are people. allowing such "truth" questions and answers leads to discussion and debate, and usually flame wars, which isn't what StackExchange is about. SE is a Q&A site, not a discussion and debate site.
What particular groups or denominations believe is the truth is an objectively answerable question. What they believe may or may not actually be the truth, but it is what they believe is the truth. So that becomes a factual matter ("what a church believes") rather than a matter of opinion.
The problem with asking what all denominations believe is that there are far too many denominations to cover in a reasonable space. I happen to think that asking in an open-ended way for the views of various denominations can be useful. But the consensus here is that it's too broad, and leads to a "popularity contest" among denominations, which is seen as not useful. That's why the mods on Christianity.SE frown on such broad questions, even though theoretically they are objectively answerable.
Should we encourage the answerer to post their denominational viewpoint vs. closing truth questions?, 2015
Affable Geek:
The biggest risk one has with an academic site like this is the prospect of uninitiated users voting for answers they like, rather than answers that inform. I'm not a Mormon. I don't "like" when answers go to non-canonical scriptures to try to answer a question. I don't think the Book of Mormon is valid.
But that doesn't and shouldn't matter - because what this site is for is for information, not truth. I've asked many questions about the LDS church because I want to understand them better. If you're asking me to judge what I like, I'd probably discourage all the Mormons. But if you're asking me to learn, I want them here.
Ideally, when you are voting, you are saying "This answer is informative and reflective of the tradition for which it claims to speak." Downvotes mean "this misrepresents the tradition" not "I don't like it."
Encouraging truth questions makes it impossible to foster that - people will tend to vote what they think is "true," rather than what is descriptive of actual practice.
Flimzy:
So rather than asking "Is Jesus eternally God?" then receiving 75 answers with vote counts ranging from -25 for the Arian answer, -10 for the Mormon answer, and +45 for the Evangelical answer (which would roughly reflect the number of votes from each respective denomination, rather than the "correctness" of the answer), we simply require that each question ask for a specific denomination.
One thing that makes such truth questions "too broad" is the fact that they quickly amass many many answers. It becomes very hard to sift through and can become (as alluded to in the other answers) a popularity contest for the "best" answer, rather than for the most informative answer according to a limited scope. -- Mr. Bultitude
Is this question off topic now that I have edited it?, 2016
So what do you want out of the question? If you want a truth answer or to pit views against each-other so you can decide what to believe yourself you're probably on the wrong site. If that's not what you're after and you want to know more about what extant Christian teachings are and why they are that way, then I would start at the top of the question and re-write it to reflect a scope appropriate for this site from the start. -- Caleb ♦
How can anything outside of Bible, not be labeled as an opinion?, 2014
Of course I have an answer I believe to be true, but that doesn't mean all Christians agree with me. This is what we sometimes call a "truth question" and do not like to see on this site. These often get closed with the primarily opinion-based close reason, not because there are no good answers but because it is not specified whose good answers are being sought. -- Caleb ♦
What Christianity.StackExchange is (and more importantly, what it isn't), 2012
David Stratton:
This site is a place to come to learn about what various Christian teachings have to say. ... This site is not a place to come to learn which Christian teachings are true.
This site is a place to ask about, learn about, and inform about various Christian teachings, denominations, concepts, and doctrines. ... This site is not a place to debate which of these teachings are true.
This site is a source for truthful answers about doctrine, Christian teachings, theology, ... This site is not a source for Truth with a capital "T"
Affable Geek:
It is less of a church then a seminary: Imagine being observed by a bunch of professors who know the Bible, but don't necessarily believe it. That is you audience- even if many of us are believers. In seminary, "Truth" is often less important than how you arrive at it. That is not to say that Truth isn't important - it just is secondary to scholarship in this context.
Types of questions that are within community guidelines, 2014
Also, questions without a frame asking for what is true ("Truth questions") are off-topic. -- fredsbend
Tips for editing a question to make it suitable for re-opening, 2013
What I think is Truth may not be the same as what someone else thinks is Truth. To avoid endless debate that ultimately leads nowhere constructive, we simply assume that we'll never determine Truth here. -- David Stratton