(RNS) The ’Splainer (as in “You’ve got some ’splaining to do”) is an occasional feature in which the RNS staff gives you everything you need to know about current events to hold your own at the water cooler.

The attack early Monday (June 19) at a mosque overflowing with worshippers in London, which injured 11 people — and which British Prime Minister Theresa May called a "sickening" terrorist attack — occurred during the last 10 days of Ramadan, the most intensive period of the Islamic holy month.

Security forces are on high alert, as many Muslims spend the 10-day period, known as the third and final "ashra," at mosques, devoted entirely to prayer. And the supplications are particularly intense on Laylat al-Qadr, the holiest night of Ramadan – and of the entire year. What makes this night so special, and when does it occur? Let us ’Splain.

What is Laylat al-Qadr?

The Arabic term Laylat al-Qadr is most commonly translated to mean the Night of Destiny, Night of Power or Night of Decree. It is meant to mark the night that the Prophet Muhammad received the first revelations of the Quran.

The Quran doesn't specify exactly when Laylat al-Qadr is. That, of course, means every Ramadan brings renewed quibbling over the date. The hadith, or sayings of the prophet as remembered by his companions, say Muhammad hinted at several possible dates within the last 10 days of the Islamic holy month. Most Islamic scholars say it falls on an odd-numbered day. That would limit it to the eve of the 19th, 21st, 23rd, 25th, 27th or 29th days of the Ramadan. (On the Islamic calendar, the day actually starts at nightfall.)

Many Sunni Muslims tend to observe it on the 27th day; many Shiite Muslims believe Laylat al-Qadr falls on the 23rd day. This year, that would be June 22 and June 18, respectively.

How is it different from the rest of Ramadan?

The Quran has a short chapter titled Al-Qadr, which explains what the big deal is:

"The Night of Destiny is better than a thousand months. Therein descend angels and the Spirit by the command of their Lord — with every matter. It is all peace till the rising of the dawn."

It is, therefore, a time when God's blessings, compassion and mercy are overflowing. So Muslims believe it is the best time of the year to pray for forgiveness and blessings.

But that much can be said of the whole month of Ramadan, too. Many Muslims believe Laylat al-Qadr, though, is the night when God's divine decrees for each person are handed out to the angels. Simply put: It's when a person's fate for the next year is decided.

According to one hadith, worshippers who devote themselves to heartfelt prayer on Laylat al-Qadr will have all their past sins forgiven. This tantalizing promise has many observant Muslims on their knees in submission the entire night. Some turn away completely from worldly affairs and sequester themselves in mosques for the entire 10 days of the last ashra, a practice called "i’tikaaf." This spiritual retreat usually involves extensive prayers – beyond the already exhaustive "taraweeh" prayers most Muslims engage in during Ramadan – and steady recitation of the Quran.

Many Muslims believe their destiny for the next year is handed down in a decree (remember the alternative translations above?) from heaven on Laylat al-Qadr, so they aim to spend it in complete submission to God's will.