"Hubut" means to come down and descend, and it is the opposite of Su’ud (ascension) and sometimes it means to settle down in a certain place.
In order to explain the Hubut of Prophet Adam first we need to understand what the heavenly Garden he was living in was like and whether or not it was a Garden on earth or in a different world. One thing is for sure and that is the Garden was not eternal, therefore what is meant by the Hubut that has been mentioned in various Quranic verses is that he was expelled from the Garden that he lived in (which was a Garden on the earth) and was forced to cope with the inconveniences and difficulties of living outside the Garden.
The word Hubut in Arabic means to fall from a high place to a lower one, and is used as the opposite of Su’ud (ascension).
The Almighty has pointed to the expelling of Adam from the Garden and making him live outside it with the term "Hubut":
1- " لکم فی الارض مستقر و متاع الی حین وقلنا اهبطوا بعضکم لبعض عدو و " Then We said," Descend, you are each other's enemies!.
2- "قلنا اهبطوا منها جمیعاً فاما یأتینکم منی هدی فمن تبع هدای فلاخوف علیهم ولا هم یحزنون" We stated:" Get you down all from The Paradise; and whenever there Comes from me onto you a Guidance,] Know that [those who follow My Guidance, neither fear shall come on Them nor they shall grieve.
3- " قال اهبطوا بعضکم لبعض عدو و لکم فی الارض مستقر و متاع الی حین" Allah stated:" Get down] while [There will be enmity between you; and For you, there is on the earth an Abode as well as provision of Sustenance for a fixed time.
Also, in some verses the word Hubut can mean to settle down in a certain place and reside there. In the Quran Allah addresses the Israelites saying: "قال أتستبدلون الذی هو ادنی بالذی هو خیر اهبطوا مصراً فان لکم ماسألتم...…"
He said:" Do you want to exchange something commonplace for something that is better?" "Settle in some city to get what you have asked for!".
In order to explain the Hubut of Prophet Adam first we need to understand what the heavenly Garden he was living in was like and whether or not it was a Garden on earth or in a different world. One thing is for sure and that is the Garden was not an eternal and everlasting one, therefore what is meant by Hubut was a change in the place Prophet Adam lived, what is called 'Hubut Maghami' or decline in rank, not that he actually physically descended from the heavens. Both Quranic commentators and Philosophers have spoken about the Hubut and have mentioned theories that explain it, we will only explain the theories of the commentators:
In Tafsir Majma’ul-Bayan of the lateTabarsi, it reads: "The words "هبوط" "نزول" "وقوع" have the same meaning which is moving from a high place to a lower one, sometimes " هبوط " means settling somewhere, for example in the Quran Allah says: " اهبطوا مصراً " which means: "Go to the city and settle there…".
In this regard Allamah Tabatabai says: "هبوط means going out of and exiting the Garden and settling on Earth and beginning a life accompanied by many difficulties. What is understood from verses 24 and 25 of Surah Al A’raf (قال فیها تحیون و فیها تموتون و منها تخرجون - قلنا اهبطوا بعضکم لبعض عدو و لکم فی الارض مستقر و متاع الی حین) is that there was a considerable difference between life in the garden and outside of it. Living outside the Garden was difficult and inconvenient but when living in the Garden Adam (pbuh) did not feel hunger, thirst and experienced no difficulty.
He extends: " Even though he was not living in Paradise (which whoever enters will never be sent out), the garden Prophet Adam was living in was in the skies and not on earth"
Here, as probably will come to the mind of many, a question comes up, what is meant by the skies and a garden in the skies?"
In an other part of his Tafsir he explains the meaning of a garden in the skies saying: "Prophet Adam lived in a garden that was not in Paradise nor on earth, but rather it was in 'Barzakh' (the realm in between this world and the Hereafter)".
In regard to the Hubut of Shaytan after refusing to bow down to Prophet Adam, which has been mentioned in verse 117 of Surah Taha (قال فاهبط منها فما یکون لک ان تتکبر فیها فاخرج انک من الصاغرین), Allamah Tabatabai explains: "The sentence " فاخرج انک من الصاغرین " is emphasizing the phrase " فاهبط منها " because Hubut has the same meaning as ‘khuruj’ (to exit), and the only difference is that Hubut means to exit and decline from a certain status and rank and enter a lower one, and this shows that Hubut does not mean to exit one place and enter another but is actually referring to declining from a certain status and level to a lower one.
This also corroborates our claim that the two pronouns in the words " منها " and " فیها " refer to ‘rank’ and not the skies or Paradise.
Therefore the meaning of the verse will be as follows: Because of refusing to bow down to Prophet Adam when I commanded you, you must give up your status, which was the status of being humble and obeying my commands and you shouldn’t have shown arrogance, so go out and you are among the belittled ones."
In another place in his tafsir, the Allamah explains another important point: "Commanding Hubut is a takwini command that was done after living in the Garden and committing the mistake, therefore there was no religion at the time and no such thing as a sin and disobeying of Allah."
What the tafsir is trying to say is: The command to stay away from the tree in the Garden was an irshadi one, like when a doctor tells someone what he must not eat or drink because it may cause him problems and make him sick, not that the doctor will punish him if he does not act according to what he says (In other words, commands that Allah (swt) issues are to two types; mowlawi and irshadi, the first entails ones deserving punishment upon disobedience, while the latter is only a recommendation and is telling us what is better to do, not that disobeying it will bring about ones deserving punishment). In this case Allah has commanded Prophet Adam not to go close to the tree and not to eat from it, because if he does, it will lead to his expulsion from the garden, like cause and effect; eating from the fruit is the cause and its effect is that he will be expelled from the garden. This explanation from the Allamah clarifies what is meant by hubut and the reason for it.
Ayatollah Javadi Amoli also agrees that the Garden was in the realm of Barzakh, he extends: “Prophet Adam (pbuh) was transferred from a metaphysical realm to a physical one and such a transfer is the same as existential ascension, like the Quran that was sent down from Allah (swt) for the guidance of the people, not that it was a physical ascension (meaning that his body was transferred from one place to another), also, since this ascension was accompanied by Adam’s repentance and regret, it is also called the Hubut of Wilayah or Khilafah.”
The Hubut of Shaytan was his fall from his high rank, but Adam’s hubut was one that took place on earth in which his dignity wasn’t flawed from, meaning that he was sent to reside in a world in which Shaytan was also residing in, the difference between the two being that one lost his dignity and the rank he possessed, while the other didn’t lose out on anything.
Therefore Shaytan actually underwent two hubuts: 1- Descending from the great status of the angels after refusing to bow down to Prophet Adam which has been mentioned in verse 177 of Surah Taha (قال فاهبط منها فما یکون لک ان تتکبر فیها فاخرج انک من الصاغرین) 2- Descending from the Garden which was his temporary abode and coming to a lower place after tricking Prophet Adam and Eve into eating from the tree. After the mistake Shaytan was sent out from the Garden along with Adam and Eve.
In Tafsir Nemouneh we read as an answer to this question that even though some verses say that the Garden he was in was Paradise, but it seems that it was only one of the Gardens of the green and flourishing parts of the earth. Because first of all: Paradise is an everlasting and eternal blessing, meaning that if one makes it into Paradise he will never be expelled from it. Second of all: there is no way Satan can get in to Paradise for it is no place for such an evil creature, let alone having the power to tempt people and deviate them there.
Third of all: There are ahadith narrated from the household of the Prophet that back this opinion.
A narrator narrates: "I asked Imam Sadiq (as) about the Garden Adam was living in, the Imam answered: "It was one of earth's Gardens that the Sun and the Moon would shine on, and if it was Paradise he would have never been expelled from it (because Paradise is an everlasting blessing)."
Anyway, there are many clues showing that the Garden was not Paradise, because Paradise is the end of good and pious individuals, while Prophet Adam (pbuh) had just started his life there. The Garden he lived in was place were he could do good deeds but on the other hand
In another part of the Tafsir we read that Hubut means coming down because of being forced to do so, like the falling of a stone from a high place, and when the word is used for Humans it means to be forced to come down as a punishment.
Considering the fact that Prophet Adam was created to live on earth and the Garden was a only a flourishing part of the earth, therefore the Hubut of Adam refers to decline in rank and state, not a physical decline and ascension. Meaning that Allah gave lowered his rank due to his mistake and he was subsequently deprived of all the heavenly blessings and had to cope with the difficulties of living outside the Garden. 
 Al-Ein, vol. 4, pg. 44, pg. 21; Lisanul-Arab, vol.
 Of course the expulsion of Prophet Adam (pbuh) and Hawwa (Eve) from the garden wasn’t as a punishment, because we have reasoning that none of the prophets can ever commit anything wrong, and anyone who says it is possible for them to be punished has wronged them and accused Allah of something terrible. Indeed Allah (swt) expelled Adam from the garden because by eating from the forbidden fruit, things changed and His wisdom called for him to bring them to the earth and have them experience the hardships and adhere to the rulings of this world. Majma’ul-Bayan, vol. 1, pp. 196-197.
 Al-Mizan, vol. 1, pg. 135; Farsi translation of Al-Mizan, vol. 1, pg. 208.
 Farsi translation of Al-Mizan, vol. 1, pg. 213.
 Farsi translation of Al-Mizan, vol. 8, pg. 35.
 Ibid, pg. 137.
 Tafsir Tasnim, vol. 3, pg. 383.
 Tafsir Tasnim, vol. 3, pp. 374, 408 and 466.
 Tafsir Tasnim, vol. 3, pp.371-375.
 Tafsir Nurul-Thaqalain, vol. 1, pg. 62.
 Tafsir Nemouneh, vol. 1, pg. 187.
 Tafsir Nemouneh, vol. 13, pg. 333.
 See: The garden of Adam, Question 273 (website: 112).