This takes two forms: physical segregation of the sexes, and the requirement for women to cover their bodies and conceal their form.
In the Muslim world, preventing women from being seen by men is closely linked to the concept of Namus. Namus is an ethical category, a virtue, in Middle Eastern Muslim patriarchal character. It is a strongly gender-specific category of relations within a family described in terms of honor, attention, respect/respectability, and modesty. The term is often translated as "honor".
A woman's withdrawal into purdah restricts her personal, social and economic activities outside her home. In other words, a woman in purdah should always remain at home. It is permissible, however, for a woman in purdah to come out of her house in extreme necessity but that is subject to certain conditions. They are:
The barbarous nations, and amongst them the Persians especially, are extremely jealous, severe, and suspicious about their women, not only their wives (hai gamētai), but also their bought slaves and concubines (pallakai), whom they keep so strictly that no one sees them abroad; they spend their lives shut up within doors (oikoi) and when they take a journey, are carried in closed tents, curtained on all sides, and set upon a wagon (harmamaxai).
The wives were hidden in wagons and litters, that is, by purdah. It is likely that the custom of veiling continued through the Seleucid, Parthian, and Sassanid periods. This tradition of Purdah is reflected in the Shahnama, the Persian chronicle in which women are generally referred to as pushide-ruyan (پوشيده رویان) "those whose faces are covered" or pardegian (پردگيان) "those behind the curtains"
Purdah was rigorously observed in Iran before Reza Shah's purdah ban. The practice was also observed under the Taliban in Afghanistan, where women had to observe complete purdah at all times when they were in public. Only close male family members and other women were allowed to see them out of purdah. In other societies, purdah is often only practised during certain times of religious significance.
Upper-class Greek and Byzantine women were also secluded from the public gaze.
In historically Islamic Arab countries, such as Saudi Arabia, purdah is a custom with cultural rather than religious basis. Even in the United Arab Emirates, where women can wear skirts and similar modest garments, Arab women often observe purdah. It is important to differentiate between purdah and hijab. Hijab is an Islamic tradition that is based on physical and psychological morality, while purdah does not necessarily conform to Islamic teachings.
Criticism of purdah has occurred historically. Purdah was criticised from within its community, for example in the 1905 story entitled The Sultana's Dream, by Bengali feminist Rokeya Sakhawat Hussain. In 1925 Marmaduke Pickthall, a British convert to Islam and translator of the Qur'an, gave a lecture in Madras titled "The Relation of the Sexes" which condemned purdah in the Indian subcontinent, and also criticized the practice of face veiling among Muslim women.
Bhimrao Ambedkar, a social reformer and the chief architect of the Constitution of India, imputed many evils existing among the Muslims of colonial-era India to the system of purdah in his 1946 book Pakistan, or The Partition of India, saying that women lack "mental nourishment" by being isolated and that purdah harms the sexual morals of society as a whole.