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:
The second, and more modern meaning, is to refer to a certain kind of head-covering, specifically, 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.
Note that the word is not Arabic in origin, but rather Persian. In Persian, chador is the word for "tent", borrowed during the Sassanid period from Sanskrit chattra, which means "shelter".
In some countries, jilbab is sometimes called by different names. For example, in Southeast Asia, the veil is called "tudung" in Malaysia and "kerudung" in Indonesia, both being derived from the Malay word for "cover".
A variant of niqab is boshiya, where the veil completely covers the face, leaving no area for women to be able to see. If they want to see, they have to lift the veil. As you can guess, it's extremely impractical and is rarely worn these days.
The word is ultimately a loan word from Arabic and is rooted in the equestrian world, where burka refers to the blanket worn by horses to keep themselves warm. However, the veil known as burka doesn't exist in Arabia; English borrowed it from Hindustani during Mughal times. In keeping with the rules of purdah (literally "curtain" in Persian), aristocratic Mughal women were rarely seen in public and kept their living quarters separate from men and guests. If they did show up, they would be seen completely covered from head to toe.
There also exists a heightened form of burka called the paranja. Until the Red October, urban Tajiks and Uzbeks of Russian Turkestan wore a burka-like garment that has, instead of simply a mesh, a long leather cloth made of horsehair that hung all the way to the knee. After 1927, the Soviet government, under the policy of hujum, forbade any practice seen as expressing religiosity and/or seclusion of women. Today, most people from the former Soviet Central Asia consider the paranja as an outdated custom.
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 khimar 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 those who live in really rural ones or when they pray (if they pray, since Lebanon has a relatively high rate of non-observance). Some parts of Morocco outright frown 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 that religious 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, however. 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 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 a 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.
- Sub-Saharan Africa 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. Its influence may arise more frequently the farther one goes to the Asian portion of the country, i.e. closer to the rest of 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 came from. Note that second-generation (and beyond) Muslim women in the West usually do not wear any kind of head covering outside of prayer.