I'm having a hard time thinking of an example, except I remember someone making a recursive joke about it once. They explained the meaning of it by using its definition, hence the joke. Something like "An X is only an X for those who already know".
What is the name for this kind of phrase?
shibboleth
noun
Today, in American English, a shibboleth also has a wider meaning, referring to any "in-group" word or phrase that can be used to distinguish members of a group from outsiders – even when not used by a hostile other group
Probably not what you're looking for, but a fun word nonetheless.
esoteric
adjective
1. understood by or meant for only the select few who have special knowledge or interest; recondite:
2. belonging to the select few.
3. private; secret; confidential.
4. (of a philosophical doctrine or the like) intended to be revealed only to the initiates of a group
The question in your title doesn't really match what's asked in the body of your question. But a possible answer to the question in your title is jargon.
special words and phrases that are used by particular groups of people, especially in their work
The Wikipedia entry for jargon adds to this by saying
The main trait that distinguishes jargon from the rest of a language is special vocabulary—including some words specific to it and, often, narrower senses of words that outgroups would tend to take in a broader sense.
In other words, jargon can include words whose meaning within a group is quite different than the meaning outside that group.
Perhaps you are remembering the somewhat recent use of the term dog-whistle. From Oxford Dictionaries:
1.1 usually as modifier A subtly aimed political message which is intended for, and can only be understood by, a particular demographic group.
There's a fair bit of discussion about the origin of this particular usage in this EL&U question and its answers. (Essentially, it's a metaphor from actual dog whistles, which are so high-pitched that only dogs can hear them, originally applied to politics in Australia and very quickly adopted throughout the English-speaking world.) This phrase came up a lot during the recent political turmoil in the UK and US.
In the 19th century, the parlance of criminals in the UK would be termed argot, the word is less popular these days but still relevant and has a broader usage.
Wikipedia defines it as:
An argot (English pronunciation: /ˈɑːrɡoʊ/; from French argot [aʁˈɡo] 'slang') is a secret language used by various groups—e.g., schoolmates, outlaws, colleagues, among many others—to prevent outsiders from understanding their conversations. The term argot is also used to refer to the informal specialized vocabulary from a particular field of study, occupation, or hobby, in which sense it overlaps with jargon.
noun
a word or phrase that has a specific or precise meaning within a given discipline or field and might have a different meaning in common usage:
Set is a term of art used by mathematicians, and burden of proof is a term of art used by lawyers.
You could make a self-referential joke like this for example:
"Term of art" is a term of art in the legal profession.
The phrase is self-referential, and you're indicating a case of self-referential humor.
Self-referential humor or self-reflexive humor is a type of comedic expression1 that—either directed toward some other subject, or openly directed toward itself—intentionally alludes to the very person who is expressing the humor in a comedic fashion, or to some specific aspect of that same comedic expression.
These are variants of Hofstadter's famous recursive-acronym, which is very influential in the computer-science domain. For instance, GNU is a recursive acronym for GNU's Not Unix.
You might be talking about a code name (sometimes code word or code phrase):
- Also called code phrase. a word or phrase assigned a meaning understood only by those who are secretly informed of it.
Popular in spy movies, these are words or phrases that sound otherwise innocuous, but indicate to the listener that you are "in the know".
It sounds like the situation you're describing is a circular definition. wikipedia
A circular definition is one that uses the term(s) being defined as a part of the definition or assumes a prior understanding of the term being defined.
And, long-shot, but maybe you were talking about an "autological word" wikipedia again
An autological word (also called homological word or autonym) is a word that expresses a property that it also possesses (e.g. the word "short" is short, "noun" is a noun, "English" is English, "pentasyllabic" has five syllables, "word" is a word).
Tautology
http://www.dictionary.com/browse/tautology
needless repetition of an idea, especially in words other than those of the immediate context, without imparting additional force or clearness, as in “widow woman.”.
an instance of such repetition.
Logic. a compound propositional form all of whose instances are true, as “A or not A.”. an instance of such a form, as “This candidate will win or will not win.”.
Can I suggest it is an instance of Hermetica. I.e. in the sense used by Umberto Eco in Foucault's Pendulum.
The Hermetica are Egyptian-Greek wisdom texts from the 2nd and 3rd centuries AD, which are mostly presented as dialogues. Ref Hermetica
So, in Eco's Foucault's Pendulum, according to an authoritative opinion, it's a joke at the expense of the hermetic characters the publishers spend much of their time with, as when it's first used it's about how they literally all have a certain look about them (Lorenza says "professional sorcerers with faces exactly like professional sorcerers", then describes them. Diotallevi quips "Facies hermetica", and from then on it's an in-joke). Ref goodreads.com/questions/463533...
Is this the first documented example of the theoretical phenomenon first hinted at by D. Rumsfeld (DR)?
Ref ...there are known knowns etc
While the focus for DR was unknown unknowns, this gave a tantalising suggestion of the possible existence of something more esoteric and exotic, an unknown known. I.e. something where you may or may not have some intuition it exists, but that you cannot detail it with any plausible specificity.
