Assalamualaikum ustaz. Can you explain the meaning of barzakh?
Waalaikumussalam wrt. wbt.,
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions, and all those who follow his footsteps until the Final day.
Barzakh is a certainty and any living creation will taste death and none that has a soul will be able to escape death. Allah SWT states:
كُلُّ نَفْسٍ ذَائِقَةُ الْمَوْتِ ۖ ثُمَّ إِلَيْنَا تُرْجَعُونَ
“Every soul will taste death. Then to Us will you be returned.” 
Imam al-Ghazali in Ihya’ Ulum al-Din (4/494) explained that death in truth is a change of situation experienced by a soul, from having its own authority on his body to losing this ability. A soul that was used to freely use its eyes to see, legs to walk, ears to hear and all of the other parts which aided him, at this time, it can no longer do any of these things.
Imam al-Qurtubi in al-Tazkirah (pg. 18) said: Scholars stated that death is not destruction or demise of a person and that he will cease to exist, rather death is the separation of severance of the connection between the soul and body, changing or moving from one situation to another situation, one place to another and it (death) is one of the greatest calamities. Death is described as a calamity according to the statement of Allah SWT:
فَأَصَابَتْكُم مُّصِيبَةُ الْمَوْتِ ۚ
“And the disaster of death should strike you.” 
Scholars said: “However, there are matters worse than death and that is getting distracted from death, turning away and forgetting death and leaving good deeds as a preparation for life after death. Furthermore, death is a reminder and lesson for those who think.” 
Death in Islam is not total destruction of a person as believed by the deviants and ignorant. Death is a move from one place to another place, from one stage to the next and from one stopover to the following stop.
Caliph Umar bin Abdul Aziz once said:
إِنَّمَا خُلِقْتُمْ لِلأَبَدِ ، وَلَكِنَّكُمْ تُنْقَلُونَ مِنْ دَارٍ إِلَى دَارٍ
“All of you are created for the eternal life. You are actually moving from one place to another place.” 
Abu al-‘Atahiyyah, a famous poet stated:
وَما الموْتُ إلاّ رِحْلَة ٌ، غَيرَ أنّهَا مِنَ المنْزِلِ الفَاني إلى المنزِلِ الباَقي
Death is but a journey from a temporary place to a place of eternity. 
A deceased who is buried in the grace is actually alive in the realm of barzakh. Receiving blessings of punishments at the beginning of eternal life in the hereafter. Whether the person is going to receive goodness or severe punishments. 
The Meaning of the Realm of Barzakh
According to the Lisan al-Arab dictionary by Ibnu Manzur: The meaning of barzakh realm is a place between this world and the hereafter before everyone is gathered in Mahsyar, which begins from the time of death until the resurrection. So, whoever dies means that he has entered barzakh. 
It is stated in Mukhtar al-Sihah: The meaning of barzakh is a wall separating two things. It could also mean anything that exists in this world and the hereafter from the time of the death of a person until he is resurrected. So, whoever dies, means he has entered barzakh. 
Al-Jurjani in al-Ta’rifat said: Al-Barzakh (البرزخ) is stated thrice in the Quran and all of them is stated as a noun. Lexically, it means something or a barrier between two things. 
Allah SWT states:
وَمِن وَرَائِهِم بَرْزَخٌ إِلَىٰ يَوْمِ يُبْعَثُونَ
“And behind them is a barrier until the Day they are resurrected.” 
Imam Ibn Kathir when explaining the meaning of al-barzakh in the above verse cited several opinions, among them are:
- Muhammad bin Ka’ab defined it as something between this world and the hereafter and not with the people from this world who can eat and drink and not with the people in the hereafter who are receiving their punishment or rewards.
- Abu Sakhr said al-barzakh is the grave and not this world or the hereafter. They’ll stay there until the day of resurrection.
- Al-Dahhak stated it is a duration between death and the day of resurrection.
- Mujahid defined al-barzakh as a barrier for them (those who died) from returning to this world. 
Imam al-Qurtubi explained the above verse saying barzakh is the realm between death and the day of resurrection. 
According to Syeikh Ali al-Sobuni, barzakh realm is the realm people go to after they die. Barzakh lexically means separator between two things. The realm after death is named barzakh. The reason is it is a separator between this world and the hereafter. 
Syeikh al-Maraghi said: “In front of them spread something that prevents them from returning to this world until Judgement Day. Here, there is a final decision for them to return to this world. If they couldn’t do so before the day of Judgement, surely, they wouldn’t be able to after it forever, for surely after the day of resurrection, a person can no longer return to this world but stay in the hereafter forever.” 
Hopefully this explanation will increase our faith in the unseen matters. Wallahu a’lam.
 Surah al-’Ankabut: 57
 Surah al-Ma’idah: 106
 See al-Tazkirah, pg. 18-19
 See Hilyah al-Auliya’, 5/287
 See Diwan Abi al-‘Atahiyyah, pg. 223
 See Fatawa Mu’asirah, 1/273
 See Lisan al-Arab, 3/8
 See Mukhtar al-Sihah, pg. 73
 See al-Ta’rifat, pg. 45
 Surah al-Mukminun: 100
 See Tafsir al-Quran al-`Azim, 5/494. Also see Ma’alim al-Tanzil, 5/428
 See al-Jami’ li Ahkam al-Quran, 6/113
 See Safwat al-Tafasir, 2/293
 See Tafsir al-Maraghi, 9/4690