The scholars have also stated as a general rule that clothing that is used to cover must be thick and opaque so that it does not show what is beneath it, and that it must be loose so that it does not reveal the contours of what is beneath it. These two conditions must necessarily apply to the jilbab as well.
The scholars have differed as to just how much the jilbab must cover. As explained above, there are two opinions on this.
The first opinion
The first opinion of the scholars is, in effect, that the jilbab or outergarment should cover everything but the face and the hands. There are two sub-opinions here. The first sub-opinion is that there must be a single garment that covers everything that must be covered. This would mean that the garment called "jilbab" must be something like the garments known as "abaya" and "chador". The second sub-opinion is that a combination of garments that cover what the jilbab is to cover may substitute for the jilbab. Specifically, these scholars permit the head to be covered by the headscarf (khimar) and the feet to covered by socks and shoes. As long as a sister covers her head and neck with the khimar, then her jilbab does not need to cover over her head, but may be like a coat, which just covers from the shoulders on down. And as long as her feet are completely covered with socks and shoes, then her jilbab does not need to come down to the ground but may come down only to the ankles. This is the majority position. We can say that according to the majority opinion of the scholars, the garment called "jilbab" is any garment that meets the following criteria:
These scholars are agreed that the jilbab is to be worn outdoors and in open public places like the market, the masjid, etc. It does not need to be worn indoors, such as in the house or a building where access is controlled. This is because the jilbab serves the purposes of asserting the Islamic identity of a sister, and of protecting her from harassment, which are concerns only outdoors and in public. The rules in Surah an-Nur ayah 31 govern the dress of the Muslim woman indoors. Thus a sister may wear the khimar and modest clothing indoors, and this is her hijab for this location. However, the jilbab is part of her hijab when she is outdoors or in open public places.
The second opinion
According to the second opinion of the scholars, the jilbab must cover the entire body except for the eyes. Just as most of the scholars who hold the first opinion allow the khimar, coat, and socks and shoes to substitute for a one-piece outergarment that covers everything but the face and hands, so most of the scholars who hold the second opinion allow multiple pieces to substitute for the one-piece outergarment or sheet that covers everything but the eyes. These multiple pieces may include a separate affixed face veil (niqab), a headscarf (khimar), a coat or cloak (jilbab), and socks and shoes. However, these scholars would strongly emphasize that the coat-jilbab is not the same as the Quranic jilbab. The Quranic jilbab must cover everything but the eyes. It should also be noted that most of these scholars also hold that Surah an-Nur ayah 31 mandates the covering of everything but the eyes around non-mahram men, even when the sister is indoors. It is not clear if these scholars would allow modest clothes, a khimar, and a niqab or if they do require the jilbab indoors (i.e., if non-mahram men are present). Sisters who prefer this opinion should consult a scholar for specific advice on this question.
Note: Some scholars of this group hold that the jilbab must be a one-piece outergarment that covers everything but the eyes. This is the position of the Saudi ulama.
Inshallah, I hope that in this essay I have proved that the Quran and Sunna do command and make obligatory the garment called "jilbab". I further hope that I have shown that the word "jilbab" in classical Arabic, and in the usage of the scholars, is a very general term that may be translated into English simply as "outergarment". Any outergarment that meets the criteria given above is a jilbab. There are many styles that are possible, and there are many outergarments in many Muslim cultures that can be used for what the Quran means by jilbab. These may be called "abaya", "chador", "djellaba", "burnous", "haik", "milaya", or a thousand other names. They may even be called "jilbab".
What we must always keep clear in our minds is that there is the Quranic jilbab, which is any outergarment that meets the criteria set out in the Shari'a; and there may also be a "cultural jilbab" that refers to a very specific style. As Muslims we are responsible for following the Shari'a not Arab culture. When a word is used in the Quran or hadiths, we need to give it the definition it has according to the Shari'a, not the definition it might have in Arab culture.
So whether you wear an abaya, a chador, a djellaba, or indeed a "jilbab", be sure that it meets the criteria of the Shari'a: