The word hijab is originated from an Arabic word hajaba means to hide or cover. Muslim women observe hijab as ALLAH has ordered them to do so. In the Holy Quran the term jilbab and Khymar is also used in relation with hijab.
Hijab is a compulsion for Muslim women
In Islam there is no specific clothing defined for Muslim women but there are some specific instructions about how to dress up. The cloths should be loss enough through which there body parts are not being highlighted then they should not wear hazy and shiny cloths which would attract a men’s attention but there is a compulsion that every Muslim should observe hijab as this is clearly stated in the verse of the Holy Quran
"O Prophet, tell your wives and daughters and the believing women to draw their outer garments around them (when they go out or are among men). That is better in order that they may be known (to be Muslims) and not annoyed..."
One of the reasons why Muslim women are told to observe hijab is clearly stated in the verse that because of hijab Muslim women would differentiate themselves from non Muslims. Another reason to observe hijab is to keep a difference between men and women. Muslim women observe hijab so that people will judge them on the basis of their skills not on the basis of their looks and appearances. Hijab also protects a woman as she hides her appearance from men so no one could think about her sexuality. That is why a woman in hijab is considered to be a pure, virtuous Muslim woman who has a strong and good moral character.