Laylat al-Qadr, Lailatul Qadr, Shab-e-Qadr, Lailat-ul-qadr

Laylat al-Qadr (Arabic: لیلة القدر‎) (also known as Shab-e-Qadr), the Night of Destiny, Night of Power, Night of Value, the Night of Decree or Night of Measures, is the anniversary of two very important dates in Islam that occurred in the month of Ramadan. It is the anniversary of the night Muslims believe the first verses of the Qur'an were revealed to the Islamic prophet Muhammad Peace Be Upon Him.

Revelation to Prophet Muhammad
Laylat Al-Qadr is the anniversary of the night that the Qur'an was revealed. Muslims believe that revelation of the Qur'an occurred in two phases, with the first phase being the revelation in its entirety on Laylat Al-Qadr to Gabriel in the lowest heaven, and then the subsequent verse-by-verse revelation to Prophet Muhammad by the angel Gabriel (Jibril in Arabic). The revelation started in 610 CE at the Hira cave on Mount Nur in Mecca.The first Surat that was revealed was Surat Iqra. Iqra means read the prophet was told to read by the angel Gabriel. Muslims should do how much worship they can on this night.

Muslims often pray extra prayers on this day, particularly the night prayer. They awake, pray, and hope God will give them anything they may desire on this night. Mostly, they perform tilawat (reading the Qur'an).

Those who can afford to devote their time in the remembrance of God stay in the mosque for the final ten days of Ramadan. This worship is called Iʿtikāf (retreat). They observe fast during the day and occupy themselves with the remembrance of God, performing voluntary prayers and studying the Qur'an, day and night, apart from the obligatory prayers which they perform with the congregation. Food and other necessities of life are provided for them during their stay in the mosque. Devoting time to remember God, Muslims also hope to receive divine favors and blessings connected with the blessed night(laytul qadr)

Laylat al-Qadr is to be found in the last five odd nights of the 3rd decade of Ramadan. There is no history in the Qur'an as to when the specific date is.[1][2]Therefore in the Sunni communities of all the Islamic countries, the Laylat al-Qadar is found to be on the last nights of Ramadan. Mostly it is on one of the odd nights, i.e., 21st, 23rd, 25th, 27th or 29th night. And most probaly it falls on the 27th night of Ramadan. It is the night when Quraan was revealed (as a whole on the 4th sky) and then was revealed piecemeal on the Holy Prophet Muhammad (PBUH) in 23 years, 10 years in Makkah and 13 years in Madina. Quraan says about Laila tul Qadr in Surah Qadr that this single night is better than thousand of months! So Muslims remain engaged whole nigh in prayers and seek jannah for them.

Importance

Quran
We have indeed revealed this (Message) in the Night of Power:
And what will explain to thee what the night of power is?
The Night of Power is better than a thousand months.
Therein come down the angels and the Spirit by Allah's permission, on every errand:
Peace!...This until the rise of morn!
—Sura 97 (Al-Qadr), āyāt 1-5[3]

The verses above regard the Night as better than one thousand months. The whole month of Ramadan is a period of spiritual training wherein believers devote much of their time to fasting, praying, reciting the Qur'an, remembering God, and giving charity. However because of the revealed importance of this night, Muslims strive [give more effort] harder in the last ten days of Ramadan since the Laylat al-Qadr could be one of the odd-numbered days in these last ten (the first, third, fifth, seventh or ninth). Normally, some Muslims from each community perform an Iʿtikāf in the mosque: they remain in the mosque for the last ten days of the month for prayers and recitation.