Mid-Sha'ban is the 15th day of the Muslim month of Sha'ban. Laylatul Bara'ah is the night preceding the 15th day of Shaban.
Nim Sha'ban in Iran.
Nisf Sha'ban in Arabic speaking countries.
Nisfu Sya'ban in Malay speaking countries.
Shab e Bara'at in South Asia meaning the 'Night of Emancipation'.
Berat Kandili in Turkish
Sunni observe Mid-Sha'ban as a night of worship and salvation, commemorating when God saved Noah's followers from the deluge. According to Sunni tradition, God determines the destiny of all people, including whether a person lives or dies, in the coming year. For this reason it is sometimes called the "Night of Emancipation".
ImamIbn Taymiyyah was asked about the importance of the 15th night of Sha’ban. He replied:
As for the 15th night of Shabaan, there are many narrations and Athar (quotes from the Sahabah image) regarding its virtue. It has been reported of the salaf that they prayed in this night. Therefore, praying alone on this night, having precedence in the salaf, is sufficient evidence and something of this kind surely cannot be denied.
Sheikhul Hadith Fazlur Rahman A'azami (a Hanafi scholar) writes in his balanced book titled, "Shabe Baraat: The fifteenth of Sha'ban in light of the Qur'an and Hadith": "Ibnu-Taymiyyah, a scholar notorious for refuting such things, also accepts the virtue of the night of Baraat. He says: 'So many Ahaadith and reports exist regarding the excellence of the fifteenth night of Sha'ban that one is compelled to accept that this night does possess some virtue.' Some of the pious predecessors used to specially devote this night for Salat."
only deobandis/Wahabis contend that the day is a bidah and should not have any special status.
Shias celebrates the 15th night of Sha'ban as Laylat al Bara'at and observes this night as a night of worship. Being different to sunnis they also believe that on the 15th of Sha'ban, 255 AH (868 CE), Muhammad al-Mahdi was born. Shias believe him to be the twelveth Shia Imam and also the Mahdi, a very important figure who is believed by Muslims to bring absolute peace to the world.
1. Authentic ahadeeth
Hadrat Ayesha Siddiqa reports: “One night, which
was the 15th of Shabaan, I did not find the Beloved Prophet in the house so I went in search of him. After a long
search, I found him in Baqiah (the cemetery of Madinah) offering Du’a for
the deceased and praying for their forgiveness”. (Baihaqi)
The research of Sheikh Muhammad Naasir ud – Deen al – Albaanee:
Aboo Hurayrah, ‘Aa’ishah, and other companions reported that the Prophet (peace be upon him) said: “Allaah looks upon His creation on the middle of the night of Sha’baan, and He forgives all of His creation, except for a mushrik or a quarreler.”
The Messenger of Allaah said: "Allaah the Blessed and Most High, looks to His creation on the middle night of Sha'baan and forgives all of His creation except for the one who ascribes partners to Him and the one who shows enmity." 
2. About hadeeth:
On this night, perform Nawaafil, recite the Qur’an Shareef, recite abundant Durood Shareef, Istighfaar and Kalima Tayyibah.
As for the other narrations concerning the 15th of Sha'baan (which are not authentic), the Hanafi scholar, Shaikh Mulla 'Alee al-Qaaree (d.1014H) Rahimahullah records some of these Ahadeeth:
In another narration, the following people have also been mentioned:
1. One who deals in usury (Riba),
2. One who wears his trousers below his ankle with pride and arrogance
(In Arabia, people displayed their wealth and boasted in this manner),
3. One who creates disunity among two Muslims,
4. The person who unjustly takes away the right and property of another
Muslim and has not yet rectified himself.
All these persons are not shown Mercy on this auspicious Night.
A humble appeal to seek pardon and ask Allah’s forgiveness
Also on this night the Doors of Mercy and Forgiveness are opened wide,and those who sincerely grieve over and repent for their past sins and seek forgiveness from Allah are pardoned and forgiven by the Grace of Allah the Merciful.
Each Tasbih or Du’a should begin and terminate with the recital of Durood Shareef and one who wishes for the acceptance of his Du’as should use the Wasila of Sayyiduna Rasoolullah.
Hadrat Ghawth al-A’zam, Shaykh Abd al-Qadir al-Jilani has mentioned in his famous”Gunyat-ut Talibeen” that the month of Shaban according to some narrations is related to Rasoolullah. So, it is our duty, as the Ummat of Rasoolullah to love and respect this month more than any other month (besides Ramadan). One should also offer abundantly salutations (Salaat-o-Salaam) upon the Prophet.
It is the special night of seeking forgiveness and repenting to God, remembering past sins and sincerely settling the mind that one will never commits sins in the future. All the deeds that are against Shari’ah must be totally avoided so that our Du’a and Istighfaar, hopefully, will be accepted.
On this occasion, it should be the duty of all Sunni Muslims to forgive one
another and to make sure that whatever debts owed to one another is
settled. The importance of Huqooq al-Ibaad cannot be over-emphasised as
this is among the pre-requisites for proper Ibaadat. I pray that all Muslims
humbly remember this night and try as much as possible to perform
Ibaadat and other pious deeds so that their Record of Deeds be presented
in all dignity.
Dr. Muhammad al – Jibaly said: The hadeeth indicates that this night surely has a special merit
We should note that, in the above hadeeth, the Prophet indicated that Allaah, the Most High, does not forgive on this night those who have a quarrel with others. How, then, about a person who deviates from the Sunnah and establishes bid’ahs, thereby declaring a quarrel against the Prophet himself? How would such a person be forgiven?
The conclusion drawn from Shaikhul Hadith Fazlur Rahman A'azamis book is that yes, this night has a special significance because of the various Ahadith on this topic. Though no specific number of Salat are mentioned for this night, but extra Salat can be performed (as mentioned by Ibnu Taymiyyah in the above mentioned book by Shaykhul Hadith Fazlur Rahman) but there is no authentic Hadith supporting the fast specifically of this day. Hence if someone wants to fast, they should fast on the 13th, 14th, and 15th of this blessed month or they should fast on Mondays and Thursdays of this blessed month of Sha'ban. Muslims should not 'single out' the 15th of Sha'ban for fasting.
↑al-Majmoo’Recorded by al – Bazzaar, at – Tirmithee, and others. Classed as Saheeh by Sheikh al – Albaanee in as – Saheehah, Number 1144; as quoted in ‘Festivals and Celebrations’, p. 114 by Dr. Muhammad al – Jibaly, al – Kitaab and as – Sunnah Publishing, 2nd Edition, 2005
↑This is an authentic (saheeh) hadeeth. It is recorded by Ibn Maajah (no.1390), Ahmad (no.6642), Ibn Hibbaan (no.1980) and others from a group of Companions. It is authenticated by al-Haythamee in az-Zawaa'id (8/65) saying: "Reported by at-Tabaraanee in al-Kabeer and in al-Awsat and its narrators are trustworthy" and it is further authenticated by Shaikh al-Albaanee in as-Saheehah (no.1144); as quoted in http://www.islamicawakening.com/viewarticle.php?articleID=1