A hijab as commonly understood in the English-speaking world, is the type of head covering traditionally worn by Muslim women, but can also refer to modest Muslim styles of dress in general. Similar head coverings are wimples (or wimpels) worn by Christian nuns and snoods often worn by married Orthodox Jewish women. The Arabic word literally means curtain or cover (noun), based on the root حجب meaning "to cover, to veil, to shelter". Most Islamic legal systems define this type of modest dressing as covering everything except the face and hands in public. According to Islamic scholarship, hijab is given the wider meaning of modesty, privacy, and morality; the word for a headscarf or veil used in the Qur'an is khimār (خمار) and not hijab. Still another definition is metaphysical, where al-hijab "refers to the veil which separates man or the world from God."

Muslims differ as to how "hijab dress" should be enforced, particularly over the role of religious police that are enforcing hijab in Iran and Saudi Arabia. Although some countries have enforced the hijab, others have not because of the varying beliefs that it is not mandatory to wear hijab.

en.wikipedia.org/wiki/Hijab

www.shia.org/fatima.html

islamworld.net/docs/hijabvirtue.html