The word “agnostic” was coined by Thomas Huxley in 1869. I am concerned here with what state of mind is denoted by this word not with whether agnosticism is the correct position. I think it is commonly assumed that it denotes a state of mind that is neither belief nor disbelief: we can believe in God or disbelieve in God, and thus be either theists or atheists, but in addition we can be in a state of suspended belief on the question, and thus be agnostics. There is belief, disbelief, and a kind of neutral belief—undecided belief, null belief, belief that hovers but will not land. It is sometimes thought that agnosticism is vaguely disreputable or weak-minded, as if the agnostic is someone who hasn’t got the guts to form firm beliefs. He or she hasn’t the courage to form a belief, the stakes being quite high, so chooses to dwell in a twilight zone of non-commitment. This presupposes that there is such a thing as suspended belief—a state of mind in which no definite belief is formed. It seems to me that this is the wrong way to describe the agnostic’s state of mind: the agnostic has just as firm a belief as anyone else with respect to God’s existence, viz. that there are no rational grounds for preferring theism over atheism or vice versa. The agnostic may be quite certain that this is so, as committed as any ardent believer or disbeliever—she cannot be accused of being wishy-washy on the question. She has considered the question and formed the belief that no belief either way is rational. She has a meta-belief that is as committed as any: a belief about belief. So there is no third state of belief corresponding to agnosticism—no semi-belief or uncommitted belief or suspended belief. There is simply belief. In fact, there is really only one kind of belief, namely belief: the theist believes in God, the atheist believes there is no God, and the agnostic believes that no belief on the question is rational. That’s it—no subdivisions of belief exist of the kind commonly supposed. The state of mind of any of these three categories of person is simply a state of belief; nothing further needs to be added.
The OED agrees, defining “agnostic” as follows: “a person who believes that nothing is known or can be known of the existence or nature of God”. That is, the agnostic has a belief about religious (or irreligious) belief, namely that it is not rationally warranted. There is no quasi belief or halfhearted belief or state of aporia. The definition, however, is lacking in another way: it is wrong. The agnostic need not believe that nothing is known of the nature of God, or even of God’s existence; he may accept that we know that if God exists he is omniscient, or even that God has possible existence (either in the epistemic or metaphysical sense of “possible”). What the agnostic contends is that such knowledge is not sufficient to tip the balance of argument in the direction of God’s actual existence. To think there are considerations on both sides of an argument, making it impossible to pick sides, is not to suppose that nothing can be reasonably asserted on either side. And clearly the agnostic can allow that the question of God’s existence might one day be decided; it is just that we don’t have the evidence now to justify either theism or atheism. The essence of the position is simply that nothing rationally justifies one belief over the other, not that we are condemned to complete ignorance of God’s existence or nature. Furthermore, the definition limits agnosticism to the religious sphere, but it is possible to be an agnostic about many things. You can be an agnostic about whether William Shakespeare wrote the plays customarily attributed to him, or whether Jupiter has five moons, or whether the earth is flat, or whether Roger Federer will retire within two years. You simply hold that the evidence you have doesn’t settle the matter one way or the other. There is nothing pusillanimous about holding this position, nor does it betoken a special state of mind of non-belief: it is a straightforward belief about what it is rational to believe in the circumstances. Perhaps this is why no special word existed for this state of mind before Huxley coined it—because there is no special state of mind involved (the “agnostic stance”). It is just one belief among others.
Here is an objection: what about someone who is just too lazy or poorly positioned to form beliefs on the matter at hand? If you ask his opinion on whether the Battle of Hastings was fought in 1066, he will throw up his hands and say he has no idea and doesn’t much care. He is, he tells you, agnostic on the question. It isn’t that he thinks that there is no evidence that favors one answer over another, or that the matter cannot be rationally decided. He just thinks that he, in his contingent ignorance, must remain agnostic. Two points can be made. First, he does believe that he has no evidence that would enable him to decide the matter, and this is what his professed agnosticism consists in. It is not that he is in a wavering and woolly state of mind; he will tell you that he is quite sure that he doesn’t know either way. He is not even inclined to favor one answer over the other. There are many questions like this, on which we feel ourselves uninformed and unable to offer an opinion, or we just haven’t thought about it. This is simple ignorance not considered judgment about the rational status of a debate. That is why (and this is the second point) we don’t normally call such a state “agnosticism”: it is not a considered opinion got by weighing all available evidence. It is just an admission of ignorance. The agnostic about religion is not saying that he has never considered the question of God’s existence and is hopelessly ill informed about it, as if the next thing you say might tip him in one direction or the other. So the case of the ignorant non-believer is not a counterexample to the general characterization of agnosticism being proposed. Agnosticism is always principled not casual.
This analysis is confirmed by what would otherwise be puzzling: there is no analogue of agnosticism for desire or intention. We can desire something or desire its opposite, but we can’t be in a neutral state of desire agnosticism. We can believe that nothing favors one desire over another (a peach or a plum), but we can’t have some sort of intermediate desire analogous to suspended belief. What would that desire be? Similarly, I can intend to go to the movies or I can intend to stay home, but I can’t intend something mysteriously between the two—as if I have a kind of indeterminate intention. If belief were capable of this kind of indeterminacy, we would expect that desire and intention would be; but they aren’t, so we should question that account of agnosticism. The only kind of agnosticism there is consists simply in the belief that nothing decides the question—not some kind of non-committal belief or wavering desire or indeterminate intention. It is of course possible to suspend belief (or disbelief), as we like to say, but the agnostic is not someone who is suspending his belief in God or suspending his belief in the absence of God; he has no such belief to suspend. He simply believes that nothing favors one belief over the other. It is also true that someone could be quite neutral on a question simply because it has never entered his head to consider it, so that he doesn’t have the belief that the jury is still out; but again, that is not the position of the agnostic (or else animals and little children would be agnostics). The agnostic doesn’t lack a belief; he has a belief, which is what his agnosticism consists in. The agnostic is a believer, just as the theist is, or the atheist. He indeed takes himself to be a more rational believer than the other two, not to be someone with a problem about believing—a chronic hesitator or belief-a-phobe. The agnostic is a firm believer in belief. He takes himself to knowthat belief in God is irrational, just as belief in the absence of God is also irrational. There is nothing peculiar about his belief system, as if he has trouble forming beliefs. To put it differently, the agnostic is a person who believes that faith is not the right way to form beliefs; and there is nothing more to it than that.
 It would be wrong to model agnosticism on a reluctance to say whether one is a theist or an atheist: there is indeed a third way between saying that God exists and saying that God does not exist, i.e. saying nothing (perhaps for fear of courting unpopularity). But being an agnostic is not a reluctance to form a belief; it is just a type of belief, whether one is happy to express it or not.
 To put it in the usual analytic style, the meta-belief is necessary and sufficient to qualify someone as an agnostic. The sufficiency part is important: there is no more to agnosticism than holding such a belief—no more psychologically speaking. The necessity part tells us that agnosticism is always an explicit reflective position, never just a matter of ratiocinative indolence (a community of unreflective people who have never thought about God’ existence and have no opinions on the subject cannot be described as community of agnostics). The agnostic is someone who actively rejects both theism and atheism—he firmly and positively believes both positions to be irrational. (By the way, I am myself an atheist not an agnostic.)
I agree with your characterization of agnosticism as an explicit and deliberate stance that doesn’t result from mere ignorance or indifference (uninterest).
There are two basic kinds of agnosticism as a “meta-belief”:
1. the belief that there are neither good reasons to believe that atheism/theism is true nor good reasons to believe that it is false (called “skeptical agnosticism” by Michael Martin and “zero-data agnosticism” by Theodore Drange)
2. the belief that there are both good reasons to believe that atheism/theism is true and good reasons to believe that it is false, but they are equally good and cancel each other out (called “cancellation agnosticism” by Michael Martin and “data-vs-data agnosticism” by Theodore Drange)
(Drange added “data-vs-principle agnosticism” and “unknowability agnosticism”: https://infidels.org/library/modern/theodore_drange/definition.html)
I agree: no reasons versus equal reasons.