What exactly does it mean to say something is "grammatical?"

According to Wiktionary, the adjective grammatical means:

(linguistics) Acceptable as a correct sentence or clause as determined by the rules and conventions of the grammar, or morpho-syntax of the language.

In the linked related question, Can “grammatical” mean “grammatically correct”?, Berrie England wrote:

To say that a sentence is grammatical is to say that it conforms to the rules of English grammar as found in the way in which native speakers normally use the language and... Describing any construction as incorrect is unhelpful and inadequate. That is why, in most cases, it it makes more sense simply to say whether or not a construction is grammatical.

I have seen some occasions where there are two different explanations about a grammatical issue. For example, the linked question “The earthquake, along with its subsequent aftershocks, HAS/HAVE …” asks whether it is grammatical to use have or has after "The earthquake, along with its subsequent aftershocks..."

There are two distinctly different answers posted by two users, one says we have to use has as the earthquake is the subject and along with... is a prepositional phrase, and the other says has is right, but we could consider using have as along with... has a potential to be considered as a conjunction.

Which is grammatically correct? Both of them are grammatical as long as you could quote the right reference in a grammar book.

Should we use are or is after dummy there when there are plural words following the verb? Should we use are or is after a collective noun such as family, team, etc. Can we use an indefinite article before a mass noun? Should all the English adjectives be placed before a noun? How about something special?

There are countless number of grammatical questions that could be answered in more than two ways. And some say A is grammatically correct, but B is broadly used colloquially.

What does colloquially exactly mean, then? Does it mean it is not grammatical?

I would have called you if you would have let me know it was that urgent.

Is the above sentence grammatical? Related question, “If I would have lost you” vs “If I had lost you”.

The answer is no. But it is used colloquially by some people especially in the U.S.

If A writes a grammar book that says we can use would have + PP after the conjunction if, the above sentence would be grammatical in accordance with the grammar book written by A, but it would be ungrammatical according to B, C, D, etc.

But we can't always say which book or grammar you are referring to when you say some sentences or clauses are grammatical, then, the word is as ambiguous as it gets and should be avoided unless you are sure about which grammar book you are referring to.

I think grammatical is often times synonymous with "it makes sense to my native ears" and it could be used when you talk about uncontroversial rules that are so obvious that you don't have to quote any grammar book. But saying it is grammatical should be avoided when you are not sure about what grammar rules you are referring to.

The grammatical can be defined with reference to a dialect or with reference to a language comprised of one or more dialects.

When considered as a whole, the speech acts of a preponderance of native speakers of a given dialect or language reveal a set of inherent rules these speakers are following. Utterances which conform to these rules are said to be grammatical.

When viewed at a point in time, synchronically, these rules appear to be stationary; but when viewed over time, diachronically, these rules are seen to be a moving target. And different features of a language or dialect change at different rates. So what is judged to be grammatical at one point in time may be judged to be marginal, or outright ungrammatical, a hundred years later, say. The number of speakers who follow the rule has dwindled and the number of people who violate it has grown.

Things can get a little complicated when the focus is language, not dialect. If we regard the language not as the superset of its dialects but as the subset of rules that are shared among its dialects, then what may be grammatical in a dialect might not be grammatical for the language.