The term hijab or veil is not used in the Qur'an to refer to an article of clothing for women or men, rather it refers to a spatial curtain that divides or provides privacy. The Qur'an instructs the male believers (Muslims) to talk to wives of Prophet Muhammad behind a hijab. This hijab was the responsibility of the men and not the wives of Prophet Muhammad. However, in later Muslim societies this instruction, specific to the wives of Prophet Muhammad, was generalized, leading to the segregation of the Muslim men and women. The modesty in Qur'an concerns both men's and women's gaze, gait, garments, and genitalia. The clothing for women involves khumūr over the necklines and jilbab (cloaks) in public so that they may be identified and not harmed. Guidelines for covering of the entire body except for the hands, the feet and the face, are found in texts of fiqh and hadith that are developed later.
Source : Wikipedia