The houris ( /ˈhuriz/ ) (from Persian : حوری ) or ḥūr (plural of ḥaurāʾ or ḥūrīyah Arabic : حورية ) are beings in Islam , described in English translations as "full-breasted companions of equal age [or well-matched]",  "lovely eyed",  of "modest gaze", virgins  of paradise, denoting humans and jinn who enter Jannah ( paradise ) after being recreated anew in the hereafter.  The word itself occurs four times in the Qur'an , always in the plural:
- "Thus. And We will marry them to fair women with large, [beautiful] eyes",
- "They will be reclining on thrones lined up, and We will marry them to fair women with large, [beautiful] eyes",
- "Fair ones reserved in pavilions",
- "And [for them are] fair women with large, [beautiful] eyes"
but they are also referred to in a few other passages in different terms.
In the Quran, the houris are called "companions", described as being "restraining in their glances" (chaste),   with "modest gazes", "wide and beautiful/lovely eyes",    "eyes like pearls",  and "full-breasted". 
To Shia scholars, the most important fact of the description of the houris is that good deeds performed by believers are recompensated by the houris, which are the physical manifestations of ideal forms, that won't fade away over time, and who will serve as faithful companions to those they accompany.
Details of the houris that have been pointed out by Sunni scholars include that the houris would not urinate , defecate or menstruate .  It has also been said that all houris are "transparent to the marrow of their bones",  "eternally young", "hairless except the eyebrows and the head", "pure"  and "beautiful".  Islamic scholars such as Ibn Majah and Al-Suyuti have also described them as having libidinous vaginas.
Classical Arabic usage
The word 'ḥūr' ( حُور ) is the plural of both ʾaḥwar ( أحْوَر ) (masculine) and ḥawrāʾ ( حَوْراء ) (feminine)  which can be translates as "gazelle-eyed" (or "having eyes with an intense contrast of white and black",) or as "distinguished by ḥawar ( حَوَر )", which itself means "intense whiteness of the eyeballs and lustrous black of the pupils". Some also propose that the most literal translation of the noun into English would be "pure companions, most beautiful of the eyes". 
Corresponding Hebrew root
In Hebrew the corresponding adjective חיוור hiwer has the same root h-w-r, meaning "pale, whitish". The corresponding word for eye is עין Ayin .
No relation between "Houri" and "whore"
The English word " whore " ( German Hure , Danish hore , Swedish hora , Dutch hoer , Proto-Germanic *hōrōn , masculine form Gothic hors , Proto-Germanic *hōraz ) is thought to stem from the Proto-Indo-European verb root *keh₂- "to love" and is not etymologically related to the Arabic ( Semitic and thus non-Indo-European) word houri . 
Description of the houris
The houris are mentioned in several passages of the Quran, always in plural form. No specifics are even given, though, as to the number of houris that should be available to each believer.
As for the gender of the houris: the Quran doesn't indicate that only men would be granted the company of houris — in fact, it can be inferred from the context that both men and women believers will have a plural number of houris for themselves.  This in turn leads to the assumptions that houris can be both male or female.
On the other hand, feminine adjectives or participles are always used when it is possible to make a distinction,  and the Qur'an says that one of the favors granted to those in Paradise is houris "untouched before them by man or Jinni",  which implies that they are (female) virgins. They are described as virgins in 56:36 (although the word in another context can mean "first-born").
Spouses of the deceased being recreated as houris
Many verses of the Quran refer to the recreations of their spouse(s) they had in their Earthly lives:
And among His wonders is this: He creates for you mates out of your own kind so that you might incline towards them, and He engenders love and tenderness between you: in this, behold, there are messages indeed for people who think! ... And He it is who creates [all life] in the first instance, and then brings it forth anew: and most easy is this for Him, since His is the essence of all that is most sublime in the heavens and on earth, and He alone is almighty, truly wise.— Quran, sura 30 ( Ar-Rum ), ayat 21...27
And, O our Sustainer, bring them into the gardens of perpetual bliss which Thou hast promised them, together with the righteous from among their forebears, and their spouses, and their offspring—for, verily, Thou alone art almighty, truly wise— Quran, sura 40 ( Ghafir ), ayah 8
The houris in the Sunni Hadith
A number of Sunni hadiths (collections of the reports of the teachings, deeds and sayings of the Islamic prophet Muhammad, accepted as canonic by most, but not all, Muslims) also mention the houris:
Muhammad al-Bukhari (810–870):
"...everyone will have two wives from the houris, (who will be so beautiful, pure and transparent that) the marrow of the bones of their legs will be seen through the bones and the flesh."— Muhammad al-Bukhari, Sahih al-Bukhari , Book 54 "The Beginning of Creation", hadith 476)
[People who enter Paradise] will not urinate, relieve nature, spit, or have any nasal secretions. Their combs will be of gold, and their sweat will smell like musk. The aloes-wood will be used in their censers. Their wives will be houris. All of them will look alike and will resemble their father Adam (in stature), sixty cubits tall.— Muhammad al-Bukhari, Sahih al-Bukhari , Book 55 "Prophets", hadith 544 
Muslim ibn al-Hajjaj Nishapuri
Muslim ibn al-Hajjaj Nishapuri (821–875):
Muhammad reported that some (persons) stated with a sense of pride and some discussed whether there would be more men in Paradise or more women. It was upon this that Abu Huraira reported that Abu'l Qasim (the Holy Prophet) said: The (members) of the first group to get into Paradise would have their faces as bright as full moon during the night, and the next to this group would have their faces as bright as the shining stars in the sky, and every person would have two wives and the marrow of their shanks would glimmer beneath the flesh and there would be none without a wife in Paradise.— Muslim ibn al-Hajjaj Nishapuri, Sahih Muslim , Book 40 "Pertaining to Paradise", hadith 6793 
— Muslim ibn al-Hajjaj Nishapuri, Sahih Muslim , Book 31 "Pertaining to the Merits of the Companions", hadith 6012 
Abu `Isa Muhammad ibn `Isa at-Tirmidhi (At-Tirmidhi) (824–892):
Al-Hasan Al-Basri says that an old woman came to the messenger of Allah and made a request, O’ Messenger of Allah make Dua that Allah grants me entrance into Jannah. The messenger of Allah replied, O’ Mother, an old woman cannot enter Jannah. That woman started crying and began to leave. The messenger of Allah said, Say to the woman that one will not enter in a state of old age, but Allah will make all the women of Jannah young virgins. Allah Ta’aala says, Lo! We have created them a (new) creation and made them virgins, lovers, equal in age.— Al-Tirmidhi, Jami` at-Tirmidhi (Surah Waaqi’ah, 35–37).
A houri is a most beautiful young woman with a transparent body. The marrow of her bones is visible like the interior lines of pearls and rubies. She looks like red wine in a white glass. She is of white color, and free from the routine physical disabilities of an ordinary woman such as menstruation, menopause, urinal and offal discharge, child bearing and the related pollution. A houri is a girl of tender age, having large breasts which are round (pointed), and not inclined to dangle. Houris dwell in palaces of splendid surroundings.— Al-Tirmidhi, Jami` at-Tirmidhi
Ibn Majah (824–887):
Houris do not want wives to annoy their husbands, since the houris will also be the wives of the husbands in the afterlife. " Mu’adh bin Jobal (Allah be pleased with him) reported that Allah's Messenger (peace and blessings of Allah be upon him) said, 'A woman does not annoy her husband but his spouse from amongst the maidens with wide eyes intensely white and deeply black will say: Do not annoy him, may Allah ruin you." He is with you as a passing guest. Very soon, he will part with you and come to us.
As Muslim ibn al-Hajjaj Nishapuri (see above), also Abu Huraira mentions houris as the solution to previous mundane worries as to whether there would be more women or more men who would go to paradise  (and whether, therefore, there would be a shortage of each gender for couple-making in the afterlife).
Abu Ubaidah ibn al Jarrah (Abu Ubayda) said that the recreated women of this life referring to
We have created (their Companions) of special creation.
And made them virgin—pure (and undefiled)— Quran, sura 56 (Al-Waqia), ayat 35-36 
were mentioned in the previous verse as houri in verse 22.
Damrah bin Habib, and Artat bin Al-Mundhir
Artat bin Al-Mundhir said regarding houri mentioned in sura Rahman (55), ayah (verse) 56:
Damrah bin Habib was asked if the Jinns will enter Paradise and he said, 'Yes, and they will get married. The Jinns will have Jinn women and the humans will have female humans.'— Ibn Kathir, Tafsir ibn Kathir
Al-Hasan al-Basri stated that the word "houri" implied the righteous women among mankind who are rewarded with paradise as related in the Tafsir of Tabari quoted by Muhammad Asad in his tafsir "Message of Quran" concerning the following ayah:
We have created (their Companions) of special creation.
And made them virgin—pure (and undefiled)— Quran, sura 56 (Al-Waqia), ayat 35-36 
Muhammad ibn Jarir al-Tabari mentions that all righteous women, however old and decayed they may have been on earth, will be resurrected as virginal maidens and will, like their male counterparts, remain eternally young in paradise.
Ibn Kathir says that the houris "are delightful virgins of comparable age who never had sexual intercourse with anyone, whether from mankind or Jinns, before their husbands."  by commenting, "in the other life, after they became old in this life, they were brought back while virgin, youthful, being delightfully passionate with their husbands, beautiful, kind and cheerful."
Ibn Kathir also stated that Muhammad confirmed that there would be sexual intercourse in Paradise.
Al-Qurtubi reconciled between a previous hadith that stated that the majority of the inhabitants of Hell ( Jahannam ) would be women by suggesting that many of the women that will form the majority in Hell will be among the sinners that would stay there merely temporarily and would then be brought out of Hell, into Paradise. Thereafter the majority of the people of Paradise will be women.
Fakhr al-Din al-Razi comments that amongst the houris mentioned in the Quran would also be "[even] those toothless old women of yours whom God will resurrect as new beings"
The "large breasts" of the houris
Book 78, verse 33 of the Quran says that the houris would be large-breasted. This adjectivation, however, has not been translated into all non-Arabic versions of the Quran. 
Ibn Kathir, in his tafsir , writes that the adjective contained in said verse "means 'round breasts'." He goes on as to state that it is "meant by this that the breasts of these girls will be fully rounded and not sagging, because they will be virgins, equal in age." 
As an alternative interpretation, Muhammad Asad has said the following regarding such verse:
As regards my rendering of kawa’ib as "splendid companions", it is to be remembered that the term ka'b —from which the participle ka’ib is derived—has many meanings, and that one of these meanings is "prominence", "eminence" or "glory" (Lisan al-Arab); thus, the verb ka'ba , when applied to a person, signifies "he made [another person] prominent", "glorious" or "splendid" (ibid.) Based on this tropical meaning of both the verb ka'ba and the noun ka'b, the participle ka'ib has often been used, in popular parlance, to denote "a girl whose breasts are becoming prominent" or "are budding" hence, many commentators see in it an allusion to some sort of youthful "female companions' who would entertain the (presumably male) occupants of paradise ... This interpretation of kawa’ib overlooks the purely derivative origin of the above popular usage—which is based on the tropical connotation of "prominence" inherent in the noun ka'b —and substitutes for this obvious tropism the literal meaning of something that is physically prominent: and this, in my opinion, is utterly unjustified. If we bear in mind that the Qur'anic descriptions of the blessings of paradise are always allegorical, we realize that in the above context the term kawa’ib can have no other meaning than "glorious [or "splendid"] beings".— Muhammad Asad, The Message of The Qur'an
The authoritative Arabic-English Lexicon of Edward William Lane defines the singular of the word kawa`ib as "A girl whose breasts are beginning to swell, or become prominent, or protuberant",  related to words meaning knob, breast, bosom, virginity, and so forth.
Reference to "72 virgins"
The idea of 72 virgins in Islam refers to an aspect of paradise. In a Sunni collection by Abu `Isa Muhammad ibn `Isa at-Tirmidhi in his Jami` at-Tirmidhi and also quoted by Ibn Kathir in his Tafsir ibn Kathir of sura 55  it is stated:
It was mentioned by Daraj Ibn Abi Hatim, that Abu al-Haytham 'Adullah Ibn Wahb narrated from Abu Sa'id al-Khudhri, who heard Muhammad saying, 'The smallest reward for the people of Heaven is an abode where there are eighty thousand servants and seventy-two houri, over which stands a dome decorated with pearls , aquamarine , and ruby , as wide as the distance from al-Jabiyyah to San'a . 
However, regarding the above statement Hafiz Salahuddin Yusuf has said: "The narration, which claims that everyone would have seventy-two wives has a weak chain of narrators."
In the same collection of Sunni hadiths, however, the following is judged strong ( hasan sahih ):
That the Messenger of Allah said: "There are six things with Allah for the martyr . He is forgiven with the first flow of blood (he suffers), he is shown his place in Paradise, he is protected from punishment in the grave, secured from the greatest terror, the crown of dignity is placed upon his head—and its gems are better than the world and what is in it—he is married to seventy two wives among the Hur the `Iyn ["wide-eyed ones", اثْنَتَيْنِ وَسَبْعِينَ زَوْجَةً مِنَ الْحُورِ الْعِينِ] of Paradise, and he may intercede for seventy of his close relatives."