Leila is the Hebrew and Arabic word for "night", laylah (לילה) (written as ليلة in Arabic). The identification of the word "night" as the name of an angel originates with the interpretation of "Rabbi Yochanan" (possibly Yochanan ben Zakkai, c. 30–90 AD) who read "At night [Abraham] and his servants deployed against them and defeated them” (Genesis 14.14, JPS) as "by [an angel called] night" (Sanhedrin 96a).
The story of Qays and Layla or Layla and Majnun is based on the romantic poems of Qais Ibn Al-Mulawwah قيس بن الملوح, who was nicknamed Majnoon Layla (Arabic: مجنون ليلى)(Arabic for madly in love with Layla) to his cousin Layla Al-Amiriah ليلى العامرية in 7th century Arabia, his poems are considered the paragon of unrequited chaste love, they later became a popular romance in medieval Iran, and use of the name spread accordingly; the name also gained popularity further afield in the Muslim World, amongst Turkic peoples and in the Balkans and India.
Variant spellings include Laela, Laelah, Laila, Layla, Leïla, Leighla, Lejla and Leyla.
In the Nordic countries, Laila or Lajla (pronounced lie-lah) is derived from the Sami name Láilá, the Sami variant of Helga which means holy.