From Wiktionary, the free dictionary
From Arabic لَيْلَةُ الْقَدْر (laylatu l-qadr), from لَيْلَة (layla, “night”) and قَدْر (qadr).
Laylatul Qadr
- (Islam) A night during Ramadan that commemorates the initial revelation of the Qur'an, usually on the 27th of Ramadan.