There isn't one and never has been, so this could be a very short ZGBlog.
The term is used, however, by people who believe in myths (that's a large number) so perhaps it is worth a few remarks. It was used against me recently by a government junkie on the News Hour forum, who wanted me to accept that government has brought me benefit, for which I should be grateful. He worked himself up into quite a frenzy, even calling me rude names!
The term is perhaps best known as the title of a work by Jean-Jacques Rousseau, who tried to figure out how a population should relate to its rulers. He lived under King Louis XV of France, and wrote it in 1762. I have a small measure of sympathy for him, because he rightly sensed that all was not well.
Louis XV had his army fight a lot of wars, notably the Seven Year War in which he lost a swath of American land to Spain, and it all cost a bunch of money. All the while, his Court (the ruling class) was living in immense luxury while those ruled were deep in poverty. The State of France, under that King, was heading for trouble; it came, in spades, a quarter century later.
Rousseau theorized that there exists or should exist an implied contract, between a people and its government, by which the former gives up some of its natural right to liberty, in exchange for the services of the latter in enforcing the remainder. However, he failed to think outside the box. He assumed that government was a fixture; it might need serious reform, but the idea that it should or might disappear altogether seems not to have occurred to him.
Alternatively perhaps it did, but he realized (no doubt correctly) that if in any way he suggested that the King and his coterie should go out of business, the survival of his career, reputation and life would be in serious peril. So he went for reform, not abolition. Many since have done likewise.
Rousseau's idea of an agreement between ruler and ruled would be an improvement on the existing absolute monarchy in France, but it's purely theoretical and incapable of being implemented. Why would an existing ruler sign it, thereby surrendering a large part of his power?
Then, how exactly would "the people" sign it - and I don't refer just to the awesome task of collecting several million John Hancocks, but rather, how does one get unanimity among those millions, when it's hard enough to get consensus in a room of a dozen people? And what happens when someone new is born; he or she will sign it when reaching some mature age, but suppose he disagrees with its terms? It simply can't be done. Coercion would be needed, perhaps upon a large minority. And coerced contracts are not contracts at all; there is no "meeting of minds."
Faced therefore with an obviously malfuntioning real society (France in the 1760s) Rousseau tried to justify a continuation of the State by imagining an idealized one - but Utopian. One that is not possible to implement for real, and which would not survive a week even if it were. How very tragic that during the very time he was writing up his theory, other Frenchmen were favoring the idea of Laissez Faire (Let us alone, to run our own affairs!) that has been first heard in 1681 from merchants fed to the teeth with State interference by Colbert and which was currently being explored by the Physiocrats, businessmen who recognized that Nature did very well when left alone and reasoned that traders would, too.
So much for Rousseau's idea of an implied contract; a fiction, a theoretical construct, an idea of what might make for a stable governed society. How now about the real one, set up a quarter century later, across in America? - does not the US Constitution (USC) provide just such a contract? "We the people... establish" a government, it begins.
Not exactly. A contract is an agreement, between two or more parties. Each signs it, to confirm acceptance of its terms. Businesslike ones are written down; oral contracts work also, but are much harder to enforce, should the parties disagree later - and "implied" ones are hopelessly vague. So who are the parties to this alleged contract, drafted in Philadelphia?
Since it starts "We the people..." it appears that the population of the former American colonies form one of the parties. All four million of them. But when we skip to the signature page, we find only 39. So only one person in a hundred thousand was actually a party to this alleged contract. Not "the People" at all. Obviously, the other 99,999 could not be held to its terms, for they did not sign.
"Aha!" it might be said; "No matter, for the 39 represented the 4 million. The power to enter contracts had been delegated by them to the 39."
Again, not exactly. First, the 39 had been elected in their several states by majority votes only; there was a substantial minority who had not voted for them at all. And of those who did vote for them, there is no evidence that there was any delegation of power to commit them to without limit - such terms as are spelled out precisely in the text. In fact, when the draft was offered back to the State legislatures for ratification, the same problem occurred; not a single State Rep had been elected by a unanimous vote and empowered to sign any binding contract he saw fit. And we know that ratification was by no means unopposed; there was a sizeable minority not wishing the FedGov to come into existence as specified. Hence again, all 4 million People did not agree to the terms of this "contract" and therefore they were not all bound by its terms. To submit dissidents to them anyway required coercion.
Furthermore, upon looking at the delegation of power the People supposedly granted someone, we see the first to be an authority to levy taxes. Trouble is, not one of the 4 million possessed the power to tax anyone; therefore none of them could delegate that power, via representatives or in any other way. The entire structure of the document is bogus!
There's worse: even if all 4 million had been unanimous in accepting the terms of the USC, they are all now dead. By what possible process can those terms be binding upon us, more than two centuries later?
And worse yet: so far we've looked only at one of the parties - the People. What about the other party? Who was that? Again look at the signature page and drink in the amazing fact: there isn't one! Contracts must always have more than one party, and this one does not. Therefore, it is not a contract. It may have some kind of meaning, but an agreement it is not.
There is, however, an unilteral contract in actual operation, and its terms appear here. Enjoy!