A houri, or hawra’ in Arabic, is the term for a beautiful virgin or nymph who awaits the devout Muslim in the paradise of afterlife. According to the Qur'an (55.56), houri have never been touched by man or jinn.
Many Muslims and non-Muslims alike believe that terrorists who commit murder and suicide in the name of Islam do so in order to gain instant admission to heaven, where they will enjoy the pleasures of the houris, although many Muslim scholars consider the passages in the Qur'an detailing the existence of houris in heaven as allegorical, not literal.
This belief in an afterlife replete with houris is based upon a hadith:
"collected by Imam at-Tirmidhi in "Sunan" (Volume IV, Chapters on "The Features of Heaven as described by the Messenger of Allah", Chapter 21: "About the Smallest Reward for the People of Heaven", hadith 2687) and also quoted by Ibn Kathir in his Tafsir (Koranic Commentary) of Surah Rhman (55), ayah (verse) 72:
"It was mentioned by Daraj Ibn Abi Hatim, that Abu al-Haytham ’Adullah Ibn Wahb narrated from Abu Sa'id al-Khudhri, who heard the Prophet Muhammad (Allah's blessings and peace be upon him) saying, 'The smallest reward for the people of Heaven is an abode where there are eighty thousand servants and seventy two wives, over which stands a dome decorated with pearls, aquamarine and ruby, as wide as the distance from al-Jabiyyah to San'a."1
Houris also appear in Ba'hai literature, and is the word given for engravings of women in ancient stonework such as the temples at Angkor Wat.