A dream about a door is usually a dream about transition, and the three traditions that read dreams most carefully agree on that much before parting ways. The tradition associated with Ibn Sirin tends to read the door as an opening into what is permitted to you, and its meaning depends on which side of it you find yourself.
That is the short answer. The longer one is more interesting, because a door is one of the few symbols where the interpreters disagree not about the mood of the thing but about what kind of thing it is at all.
The door in the tradition of ta'bir
The interpretation tradition associated with Ibn Sirin treats the door with unusual care. He was born in Basra and died in 728, a tabi'i remembered as a jurist and a traditionist, and the ta'bir attached to his name is conditional by its own admission: interpretation is analogy, not knowledge of the unseen. Many works circulating under his name were compiled long after his death, so it is safer to speak of the tradition associated with him than of his personal rulings.
Within that tradition, a door is rarely just a door. It is the boundary of a house, and a house is one's household, one's privacy and one's standing. A closed door can be read as a matter held back. An open one as access granted, or as something you are being invited to walk through before the invitation is withdrawn.
The reading is morally attentive rather than predictive. The tradition asks what the dreamer was doing at the threshold, not what fortune is approaching. A dream of standing at a door you are not permitted to enter is a dream about limits, and limits are treated as real, sometimes as mercy rather than punishment.
Artemidorus: context before symbol
Artemidorus of Daldis, writing the Oneirocritica in the second century, would have refused the question as posed. For him a symbol has no fixed meaning. The same dream means one thing to a sailor and another to a magistrate, and the interpreter's first job is to know the dreamer's trade, status, health and habits.
He separated the meaningful dream, oneiros, from the enhypnion, which merely reflects the dreamer's present state. A door in an enhypnion is not about anything. It is the noise of the house. Only when the door carries weight does it become evidence.
Once it does, Artemidorus reads it situationally. A door is an entry, and who is permitted to enter and who is shut out is a question about reputation and household. His method is closer to a field researcher's than a mystic's: gather the particulars, then interpret. A merchant dreaming of a door left ajar and a soldier dreaming the same thing are not having the same dream.
Freud and the door as disguise
Freud, in Die Traumdeutung of 1900, would have agreed with Artemidorus that the surface is not the message, though for different reasons. For him the manifest content of a dream conceals latent content, and the disguise is made by condensation, displacement and secondary revision.
The door therefore is not simply a door. It may stand in for something the dream could not state directly, and the feeling attached to it (locked, opening, half-closed) is a better clue than the object itself. His own survey of earlier writers opened with Artemidorus, whom he treated as a predecessor rather than a rival, though the method he built is backward-looking rather than predictive.
Freud's method asks what a dream is hiding. Artemidorus asks what it is reporting. The tradition of ta'bir asks what it is asking of you.
That is the real disagreement, and it is worth naming plainly. One lens treats the door as a report on your circumstances, one as a disguised wish, one as a condition to be read with humility. None of them promises to tell you what will happen tomorrow.
Where the three disagree, and why it matters
The trouble with most dream dictionaries is that they answer as though all three traditions were the same tradition, flattened into a single verdict: door equals opportunity. None of these sources says that.
The tradition associated with Ibn Sirin holds that a door read correctly tells you something about permission and limit, and that reading wrongly is a real error. Artemidorus holds that the answer depends entirely on who is dreaming, so a general verdict is not an answer at all. Freud holds that the door is not the point, and that whatever the dream says about the door is a compromise between what you want and what you can bear to admit.
So the same image can be an invitation, a condition, or a cover story. That is not vagueness. It is what happens when three careful readers of different centuries look at the same threshold and see three different things.
Reading your own door
Ask which side you were on. A door between you and something, a door you opened, a door you could not shut: the position is often more telling than the object.
Ask what was behind it, and whether you were afraid of it or drawn to it. Ask whether the door was yours to open. These are not diagnoses. They are the questions the traditions would put to you before saying anything at all, and they are the questions a single-answer dream dictionary skips.
If the dream keeps returning, or comes with waking dread, it is worth saying plainly that a professional is the right address for that. A symbol's meaning is one thing. Distress is another, and it deserves a person rather than a page.
But for the dream you woke up with this morning, the one you typed into a search bar before you had properly opened your eyes, start with the door itself. Which side of it were you standing on, and who was holding it open?