Muslim woman with Hijab

A hijab or ḥijāb (/hɪˈdʒɑːb/, /hɪˈdʒæb/, /ˈhɪ.dʒæb/ or /hɛˈdʒɑːb/;[ Arabic: حجاب‎, pronounced [ħiˈdʒæːb] or [ħiˈɡæːb]) is a veil that covers the head and chest, which is particularly worn by some Muslim women beyond the age of puberty in the presence of adult males outside of their immediate family. It can further refer to any head, face, or body covering worn by Muslim women that conforms to a certain standard of modesty. Hijab can also be used to refer to the seclusion of women from men in the public sphere, or it may embody a metaphysical dimension - Al-hijab refers to "the veil which separates man or the world from God".

Most often, it is worn by Muslim women as a symbol of modesty, privacy and morality. According to the Encyclopedia of Islam and Muslim World, modesty in the Quran concerns both men's and women's "gaze, gait, garments, and genitalia." The Quran admonishes Muslim women to dress modestly and cover their breasts and genitals. Most Islamic legal systems define this type of modest dressing as covering everything except the face and hands in public. These guidelines (for covering of the entire body except for the hands, the feet and the face) are found in texts of fiqh and hadith developed after the revelation of the Quran but, according to some, are derived from the verses (ayahs) referencing hijab in the Quran. Many believe that the Quran itself does not mandate that women wear hijab.

The term hijab in Arabic literally means “a screen or curtain” and is used in the Quran to refer to a partition. The Quran tells the male believers (Muslims) to talk to the wives of Muhammad behind a curtain. This curtain was the responsibility of the men and not the wives of Muhammad. This leads some to claim that the mandate of the Quran to wear hijab applies to the wives of Muhammad, not women generally. Αlthough hijab is often seen by critics as a tool utilized by men to control and silence women, the practice is understood differently in different contexts.

In Islamic texts - Quran
The Quran instructs both Muslim men and women to dress in a modest way:

"Tell the believing men to lower their gaze and be modest" (surah 24:30)

The clearest verse on the requirement of the hijab is surah 24:30 - 31, asking women to draw their khimār over their bosoms.

And say to the believing women that they should lower their gaze and guard their modesty; that they should not display their beauty and ornaments except what (must ordinarily) appear thereof; that they should draw their khimār over their breasts and not display their beauty except to their husband, their fathers, their husband's fathers, their sons, their husbands' sons, their brothers or their brothers' sons, or their sisters' sons, or their (Muslim) women, or the slaves whom their right hands possess, or male servants free of physical needs, or small children who have no sense of the shame of sex; and that they should not strike their feet in order to draw attention to their hidden ornaments. (Quran 24:31)

In the following verse, the wives of Muhammad are asked to wear clothes (when they go out), as a measure to distinguish themselves from others, so that they are not harassed. Surah 33:59 reads:

Those who harass believing men and believing women undeservedly, bear (on themselves) a calumny and a grievous sin. O Prophet! Enjoin your wives, your daughters, and the wives of true believers that they should cast their outer garments over their persons (when abroad): That is most convenient, that they may be distinguished and not be harassed. [...] (Quran 33:58 - 59)