Like many religions, Islam commands its followers to dress "modestly", and as a result, various items of clothing have developed that are now considered emblematic of Islam. There is often a great deal of confusion among non-Muslims—and even Muslims!—regarding these, as the wide variation in Muslim cultures has resulted in a similarly varied number of interpretations of both what must be covered to be modest and how to do so.
Before we begin, we should note that Islam requires modesty of both men and women; it's simply that the requirements for men are rather more clear-cut and a bit more revealing than requirements for women. Men are required to cover at least everything "from navel to knee"; shorts are therefore technically banned. Most Muslim societies tend to frown on men going bare-chested in public, as well. For example, some particularly fervent Muslim men opt to play sports wearing tracksuits. Furthermore, many men see it as sunnah (commendable tradition of The Prophet Muhammad) to wear some kind of head covering; this usually takes the form of a kind of skullcap called a taqiyah which looks rather like a large yarmulke.
That said, it is true that the rules for women are rather more restrictive. Consensus among traditionalist clerics is that Muslim women must, while in public and while praying, cover their whole body except for the hands and the face. Some clerics are of the opinion that the hands and face except the eyes must be covered; others are of the opinion that feet up to the ankle can be shown (a relief in many Muslim countries where some poor folk cannot afford shoes). More liberal/reformist muftis are of the opinion that modesty must be determined relative to the society and can change over time; thus, in some countries, liberal but observant women might not wear a head covering in most situations, but carry one around for prayer and entering mosques (it is undisputed that Muslim women must cover their hair while praying; Jewish doctrine is much the same, Catholicism required this well into the 20th century, and this remains a requirement in Orthodox Christianity). And of course, Islam can be quite a personal religion; theoretically, anyone can interpret The Qur'an and other religious texts for him or herself.
And finally, we'd be remiss in not mentioning: these garments are really good for disguising your appearance. Even ordinary headscarves can make you look unrecognizable, so naturally there's a lot of room for making that look as good as possible.
The result of this is a bewildering array of variations on the theme, causing confusion for many. The most common ones are what follow:
HijabThe hijab is, in theory, the generic word for "modest dress" in Islam. The word actually simply means "curtain" in Literary Arabic; indeed, never once does the Qur'an apply this term to any of the modest clothing worn by women, which is called "jilbab" (see below), while the head covering itself is called "khimar" (again see below). The hijab instead applies to the modest dress for women and men.
However, over time, Muslims have come to use the word hijab to mean a head-covering. It can generically mean any old head covering, including all of the ones listed below; most commonly, however, the word is used to mean a relatively simple scarf that leaves the whole face uncovered. There are hundreds of ways to wrap and fasten these around the head, with the result that a woman's hijab can be very personalized indeed: loosely wrapped, tightly wrapped, showing a bit of hair, one-piece (a single cloth wrapped around the head) or two-piece (a common form in the Arab World and Turkey, with a tubular under-scarf worn rather like a hat, over which is layered a fairly thin scarf going over the back two-thirds or so of the under-scarf for a sort of two-tone effect), stuffed with starched fabric, and so on. The actual material can also vary widely, and can be quite prettily decorated indeed (for instance, rows upon rows of sequins are a perpetually popular decoration among young women).
These have drawn criticism from conservative clerics on the ground that the decoration is immodest and therefore defeats the purpose of the exercise. The same criticism is, oddly, often levied by Muslim feminists who want to ditch the hijab altogether. The same odd alliance also critiques the fairly common practice among young Muslims in the West and among the rising middle classes of the Muslim world of wearing this sort of hijab with clothes that technically fulfill the requirement of covering everything while still being quite revealing of one's figure (e.g. skinny jeans and tight sweaters). As you might have guessed, this is the least conservative sort of hijab in most communities, asides from some old-fashioned ones that look like ordinary if floppy women's hats and for the most part went out of style decades ago.
KhimarThis is the Qur'anic word for the headscarves worn by women, i.e. what people nowadays refer to as "hijab". However, in the modern world, this term has evolved to refer specifically to a slightly more old-fashioned and conservative sort of hijab, consisting of a square or circular piece of cloth with a hole in the middle for the woman's face, leaving it (again) totally uncovered, but with cloth nearly to the navel in some cases. Usually light-colored.
ChadorAn Iran-specific version of the khimar, with the difference of being much larger and usually black. It reaches all the way to the ground, and thus fulfills the Iranian government's modesty requirement; however, it is not required by law as is often stated in foreign media. Note that the word is not Arabic in origin, but rather Persian; there is evidence that pre-Islamic societies of Iran had used the word to refer to a women-specific clothing, though unconnected to the current chador.
AbayaNot a head covering, but rather a loose-fitting, ankle-length sleeved robe, usually paired with a head covering. Most common in Arab countries; it is more or less required by law in Saudi Arabia. It is not restricted to women; while the styles of abaya are different for men and women, they are considered to be the same kind of garment and have the same name.
JilbabThis word is used in the Qur'an to refer to the modest garment used by Muslim women, and still is today, although different countries have interpret this differently. In Southeast Asia, in particular, a jilbab is used to mean a variety of hijab designed for practical use; something than one can simply throw on the head if one needs to answer the door, say. They're not usually too garishly decorated, but some styles of Jilbab has made inroads with the Muslim fashion industry.
ManteauA Western-inspired garment (the word is French) that fulfills the requirements for hijab, other than the head. It's just a long overcoat that conceals the legs and covers the arms. A headscarf and manteau is liberal public dress for women in Iran; they are also common among observant Syrian women.
NiqabA veil for the face, covering everything below the eyes, connected to a headscarf in various different ways. These are controversial even among relatively conservative Muslims, as the idea that women's faces must be covered is not particularly widespread. They are actually banned in some Muslim countries as a threat to public safety (not being able to see the face is a serious problem, after all), and one leading religious university, Egypt's Al-Azhar, actually banned them on campus, mostly for security reasons but also on the grounds that they were (get this) of dubious Islamicity. On the other hand, the Saudi religious police are known to harass women who do not cover their faces, even though it is technically legal. They have also caused problems for Muslims in the West; a woman in America who tried to get her driver's license photo while wearing one was denied for obvious reasons, and France, citing both cultural and security concerns, banned them entirely. The Niqab is only slightly more widespread in the Gulf, and they are more closely associated with traditional-leaning women.
BurkaOr burqa or burkha.... Traditionally associated with Afghanistan, this garment is much like a chador, but rather than leaving the face clear, it covers the whole face, leaving a net or mesh of cloth around the eyes so the woman can see. This is by far the most conservative garment of the bunch, and one of the most controversialnote ; several Muslim countries have banned it in schools or even outright. It is also banned in France, as a result of banning anything that wholly conceals one's face.
Again, like the chador, the word is not Arabic in origin but Persian, and might had referred to a woman-specific clothing in pre-Islamic Khorasan (ancient Afghanistan).
How often does one use them?As a style that can be variously interpreted, different Muslim women apply the dress differently, not only according to personal opinion but whether the government sanctions them or not. There are precisely two countries that mandate women within their territory to wear head coverings and modest dress while in public. Those are:
- Saudi Arabia
As for what kind of hijab is used, the situation is generally like this:
- Moderately religious Arab women usually wear hijab, or rarely khimar (usually reserved for the elder ones), with a modest dress of their choice; women from the Arabian Peninsula would specifically wear the abaya, for example. More conservative women wear the niqab, while old aristocratic Arab women may continue to wear the floppy hats (except when they're praying, when they may wear a simple scarf or a khimar). This is not a fixed rule, though; Lebanese women, due to having substantially more western influence, rarely wear the hijab except for the really rural ones and when they pray (if they pray, since Lebanon has a relatively high rate of non-observance). In some parts of Morocco outright frowns upon women who wear them (as it's a sign of of "Arab colonialism", since Berber identity is embraced upon there), although again women still cover to pray.
- While Iranians are obliged to wear headscarves, those who are not religious enough are permitted to simply drape them around their head, leaving the front part of the hair uncovered, babushka-style. This Iranian style of wearing hijab has sometimes been derided for being insincere and half-assed, but its simplicity has made it popular for Muslim women who are still unsure in wearing hijab properly. It has also been popularly adopted by other countries with significant influence of Iranian culture, such as Pakistan (e.g. ex-PM Benazir Bhutto), Afghanistan, and certain parts of Iraq. Meanwhile, conservative Iranian women would wear the hijab properly (i.e. with the hair covered), or go further by wearing the chador.
- The Muslims of the Indian subcontinent (except for Pakistan) and Southeast Asia, if they wear hijab at all, mostly wear the jilbab variation.
- Despite being frequently bragged upon by western media, burka is never widespread, outside of some ultra-conservative circles in Afghanistan and Pakistan, specifically those that have history of fundamentalist groups. And its reach stays there; fundamentalist groups of other places apply different headscarves, because burka, as described in its entry above, is culture-specific to the Iranian world.
- In sub-Saharan Africa, this varies. The West African Muslims don't wear the hijab (at least not the "ordinary" one), while the East African Muslims, being influenced more by Arab traders, wear it, usually in the form of abaya and hijab.
- Turkey (in)famously used to ban hijab in public places. While it is no longer the case, the hijab is not widespread, but influences may arise the farther one goes to the Asian portion of the country, i.e. the farther one goes to the Middle East.
- In Muslim-majority countries where observation of religion is not prominent, such as the Balkans or the former Soviet countries, not wearing the hijab is the norm.
- For immigrant communities in the rest of the world, the rule depends on what country they arise. Note that second-generation (and beyond) Muslim women in the West most commonly do not wear any kind of head covering outside of prayer.