What Stirner means by the term "spook" is not simply an abstract idea or concept (although it is that), but specifically a value-laden abstract idea or concept. A spook is not just an idea, but an ideal. A spook has perceived agency, requiring perceived goals and perceived values, and a spook possesses a person in such a way that the spook's ideals become their own ideals. This can be recognized in the way that spooks are so often described as spirits (which are perceived to have agency), and in the way the ideal of "Man" ("men" have agency) is another spook. All of these spooks, to be spooks, require some kind of imagined authority, because this authority is how the "spook" hijacks your values and gets you to act on its behalf. The idea of a "chair" would be a spook if anybody believed a chair to have authority. The idea of a throne is a spook if whoever sits on that throne has authority, but it is not a spook if spoken of only as an object, as a type of chair. The idea of a "hat" would be a spook if people believed a hat to have authority. The idea of a crown is a spook if whoever wears that crown has authority, but it is not a spook if spoken of only as an object, as a type of hat. The idea of a "ghost" has no authority, unless that ghost is called a god.
The word "spook" appears 50 times in "The Ego and Its Own", here is a complete, numbered list of every time the word "spook" appears, linking to it so you can see its context, and giving a short comment on its usage.
1: no context, table of contents
2: Spooks are "powers above": "the divine; i. e., of the uncanny, the spooks, the 'powers above.'".
3: Spooks are perceived spirits, a perceived consciousness: "it is the wandering seeming-body of a spirit, it is a spook"
4: Spooks are spirits: "But to you the whole world is spiritualized...therefore do not wonder if you likewise find in yourself nothing but a spook"
5: Spooks are spirits: "...since then the world has been spiritualized, enchanted, a spook."
6: no context, chapter title linked to by instance 1
7: the Christian God is being referred to as a spook: "...mysterious spook that we call highest essence."
8: in context with 7, referring to the Christian God
9: in context with 7, referring to the Christian God
10: in context with 9, as "transforming the spook into a non-spook"
11: religion is the realm of spooks: "that is religion; its realm is a realm of essences, spooks, and ghosts."
12: the Christian God is being referred to as a spook: "The longing to make the spook comprehensible"
13: Divinity is a spook: "But there always remained the contradiction of two natures, the divine and human...there remained the most wondrous spook"
14: Sin and spirituality are spooks: "In the depth of his breast dwells the spirit of sin; even the faintest thought (and this is itself a spirit, you know) may be a devil, etc. — The ghost has put on a body, God has become man, but now man is himself the gruesome spook"
15: The soul is a spook: "Man has become to himself a ghost, an uncanny spook"
16: The ideal of "man" is a spook: "To be sure, you are not Man and his true and adequate form...and you present before me...a spirit that appears, appears in you, without being bound to your body and to this particular mode of appearance — therefore a spook."
17: Spirits are spooks: "Man has not really vanquished Shamanism and its spooks till he possesses the strength to lay aside not only the belief in ghosts or in spirits, but also the belief in the spirit."
18: Spirits are spooks: "He who believes in a spook no more assumes the “introduction of a higher world” than he who believes in the spirit"
19: The ideal of "man" is a spook: "Spiritual men have taken into their head something that is to be realized. They have concepts of love, goodness, etc., which they would like to see realized.... Love is to rule. What they have taken into their head, what shall we call it but — fixed idea? Why, “their head is haunted.” The most oppressive spook is Man."
20: The ideal of "man" is a spook: "Dropping out of personal concern, one gets into philanthropy, friendliness to man, which is usually misunderstood as if it was a love to men, to each individual, while it is nothing but a love of Man, the unreal concept, the spook."
21: The ideal of "man" is a spook, explicitly as an ideal: "He who is infatuated with Man leaves persons out of account so far as that infatuation extends, and floats in an ideal, sacred interest. Man, you see, is not a person, but an ideal, a spook."
22: Value-laden concepts like "sacredness", "divinity", "holiness" are what a concept loses when it stops being a spook: "The case with regard to the spirit corresponds. When I have degraded it to a spook and its control over me to a cranky notion, then it is to be looked upon as having lost its sacredness, its holiness, its divinity, and then I use it, as one uses nature at pleasure without scruple."
23: Society as an ideal is a spook: "Society, from which we have everything, is a new master, a new spook, a new “supreme being,” which “takes us into its service and allegiance!”"
24: Spooks have their only existence in individuals: "But, although the individual is not Man, Man is yet present in the individual, and, like every spook and everything divine, has its existence in him."
25: Free will is a spook: "To be free is something that I cannot truly will, because I cannot make it, cannot create it: I can only wish it and — aspire toward it, for it remains an ideal, a spook."
26: The ideal of "man" is a spook: "As an “affair for you” there exists only my concept, my generic concept, only the Man, who, as he is called Tom, could just as well be Joe or Dick. You see in me not me, the bodily man, but an unreal thing, the spook, i.e. a Man."
27: The ideal of "man" is a spook, as is the spirit: "But, if the spirit, which is not regarded as the property of the bodily ego but as the proper ego itself, is a ghost, then the Man too, who is not recognized as my quality but as the proper I, is nothing but a spook, a thought, a concept."
28: Showing contradictions in the ideal of "man", this is difficult to understand the meaning of out of context, so click here to see the way it is used, then read up at least three paragraphs: "Men that are not men, what should they be but ghosts? Every real man, because he does not correspond to the concept “man,” or because he is not a “generic man,” is a spook."
29: The ideal of "man" is a spook, as is spirit: "Man is the last evil spirit or spook, the most deceptive or most intimate, the craftiest liar with honest mien, the father of lies."
30: Spooks are spirits: "No, you creep around to gain the spook over to yourselves, that it may fight on your side: you woo for the ghost’s favor."
31: "Right" is a spook: "Right — is a wheel in the head, put there by a spook; power — that am I myself, I am the powerful one and owner of power."
32: Spooks can have majesty and sacredness: "...there I fight against a bodily enemy; here against mankind, against a generalization, against a “majesty,” against a spook. But to me no majesty, nothing sacred, is a limit; nothing that I know how to overpower."
33: "The people", and specifically "the German people", and the "spirit" of a people, are spooks: "The people is dead. — Up with me! O thou my much-tormented German people — what was thy torment? It was the torment of a thought that cannot create itself a body, the torment of a walking spirit that dissolves into nothing at every cock-crow and yet pines for deliverance and fulfillment. In me too thou hast lived long, thou dear — thought, thou dear — spook."
34: "And, to enter more closely upon reality at once, even the best are today still persuading each other that one must have received into himself the State, his people, mankind, and what not, in order to be a real I, a “free burgher,” a “citizen,” a “free or true man”; ... And what sort of an I? An I that is neither an I nor a you, a fancied I, a spook."
35: "The people", "the people's party", and "a moral person" (in the same sense that a corporation is a legal person) are spooks: "The fact is that a moral person, be it called people’s party or people or even “the Lord,” is in no wise a person, but a spook. The fact is that a moral person, be it called people’s party or people or even “the Lord,” is in no wise a person, but a spook."
36: "The people" is a spook: "Therefore insight need go only a step farther; then it becomes clear of itself that the I of the people is an impersonal, “spiritual” power, the — law. The people’s I, therefore, is a — spook, not an I. I am I only by this, that I make myself; i.e. that it is not another who makes me, but I must be my own work."
37: "Right" and "rightness" are spooks: "If one does to us what we will not put up with, we break his power and bring our own to bear: we satisfy ourselves on him, and do not fall into the folly of wanting to satisfy right (the spook)."
38: Humanity is a spook: "The conquerors form a society which one may imagine so great that it by degrees embraces all humanity; but so-called humanity too is as such only a thought (spook); the individuals are its reality."
39: Society as a "moral person" (analogous to "legal person") is a spook: "So far one comes with the spook of society as a moral person."
40: "All" as a group of people is a spook: "But you make out of the “all” a spook, and make it sacred, so that then the “all” become the individual’s fearful master. Then the ghost of “right” places itself on their side."
41: "Man" as an ideal is a spook: "...in the ecstasy over “Man discovered at last” the egoistic cry of pain passes unheard, and the spook that has become so intimate is taken for our true ego."
42: Freedom of the press is a spook (in context): " As little as we can be declared clear of every coercion in the world, so little can our writing be withdrawn from it. But as free as we are, so free we can make it too. It must therefore become our own, instead of, as hitherto, serving a spook."
43: "Man" as an ideal is a spook: "But whoso is full of sacred (religious, moral, humane) love loves only the spook, the “true man,” and persecutes with dull mercilessness the individual, the real man, under the phlegmatic legal title of measures against the “un- man.”"
44: "Man" as an ideal is a spook: "for love to the spook or generality commands him to hate him who is not ghostly, i.e. the egoist or individual; such is the meaning of the renowned love-phenomenon that is called “justice.”"
45: Duty to self and others is spooky, the "essence" would owe it to is a spook: "But one owes it neither to himself to make anything out of himself, nor to others to make anything out of them; for one owes nothing to his essence and that of others. Intercourse resting on essence is an intercourse with the spook, not with anything real."
46: Nothing is said about spooks; the word "spookery" is used in a hypothetical.
47: "The welfare of Man" is spooky because "man" as an ideal is a spook: "It is the true welfare of “all,” because it is the welfare of Man as such (this spook)."
48: The thing that the spooky "true essence" is mocking is him as an individual: "this “true essence,” alien to me, will mock me as a spook of a thousand different names.
49: Spooks are what possess people: "if this single concept of the little word “possible” were not haunted by all the spooks of possessed men"
50: The egoist is a spook: "The egoist, before whom the humane shudder, is a spook as much as the devil is: he exists only as a bogie and phantasm in their brain."