1. Allah is God. The great majority of the non-Muslims I meet believe that Allah is a kind of personal name for some kind of small-"g" god, perhaps like Jupiter or Vulcan (gods of the Roman pantheon). I've even heard people refer contemptuously to the God of Islam as a "desert god," as if Judaism and Christianity originated in Yankee Stadium or something. The fact is that Allah is simply a compound word made from the Arabic words al (the) and lah, (god): the God. Monotheism -- the belief in a single, supreme, divine creator -- is the central and most important aspect of Islam. (And it's pronounced uh-LAH, not "Al, uh?") Even most English translations of the Qur'an I've seen do not translate the word. I believe it is really problematic and misleading not to translate such a key word for which there is an exact English equivalent.
Along these lines, I've taken several Muslims to task for using the Arabic term for God when they're speaking in English: all it does it serve to confuse those for whom it's never been made clear that Allah is the same God worshipped by Jews and Christians. Muslims may differ on various points with Jews and Christians, but this is not one of them. You'd never know, though, from the way these groups act with each other much of the time, that they each hold dear the same belief in the God of Abraham, Moses, and of Jesus (for Christians and Muslims) and, for Muslims, of Muhammad. (Muslims accept all the prophets prior to Muhammad, including Jesus. More on Jesus shortly.)
2. The biggest sin is Islam is shirk: "associating partners with God." Shirk may be generally defined as polytheism, but also includes such things as the Christian concept of a triune God, or the worshipping of anything other than God, whether it's a human being, any natural/human creation or phenomenon. This tends to create quite a theological abyss between Muslims and polytheists, but also with Christians and certain other religious groups.
You can imagine from this that expressions such as "Holy Mother of God!" give most observant Muslims the theological willies.
3. Muslims don't believe that Jesus was the son of God. As mentioned in 1, Muslims accept Jesus (in Arabic, "Isa") as a prophet, and an extremely important one at that. Following from 2, however, they do not accept the Christian belief that Jesus was the son of God (literally or ****phorically), although they do believe he is the son of Mary (in Arabic, "Maryam"). They further believe that at the time of the Crucifixion, another man was substituted for Jesus and made to look like him. Jesus was then raised up, "body and soul" by God into heaven.
This is probably the most significant point of difference between Christians and Muslims. Some Christian theologians and clergy believe that Christians err by placing too much emphasis on Jesus and elevating him to God's level, but that's an argument for another time and place.
4. Muslims don't worship the Prophet Muhammad. This naturally follows from 2, but, I suspect because of the extreme emphasis on Jesus in much of Christian practice, many assume that Islam parallels this with Muhammad and Muslims. While the Prophet is considered by Muslims to have been the human being with the best character, he is still regarded as a human being, albeit an exceptional one. And while he is regarded as the final prophet of God, he is not the only one. He does not have divine status, although Muslims hold him in the highest regard and are expected and encouraged to try to emulate his habits and characteristics, those being of the highest quality.
Muslims were for years incorrectly referred to as Mohammedans (spelled variously). This has generally become archaic, but you still see it now and then. It's actually profoundly offensive, since it implies shirk. (And while we're on it, it's Muslim, not Moslem, and Qur'an or Quran, not Koran.)
5. Translations of the Qur'an are not the Qur'an. It's well-known that something is always lost in translation. For those English speakers who don't ever expect to read the Bible in Hebrew, Aramaic, and whatever other languages in which its component texts originally appeared, it seems to be accepted that translations of the Bible are all more or less equally valid, although one may have a preferred translation. But only the Qur'an in its original Arabic is considered to be the Qur'an; translations are treated with great respect but are simply not equally valid. Muslims believe that the Qur'an was revealed to Muhammad (who was completely illiterate) by God through the angel Jibril (Gabriel). Muhammad memorized the passages as they were revealed and recited them and shared them with his family and followers. Pre-Islamic Arab culture was predominantly oral, and others ultimately learned and memorized the entire Qur'an; it was not completely written down until after the Prophet's death.
There have been many, many translations over the 1400-odd years since it was first written down; plenty of them are bad -- a few of them deliberately so in order to discredit Islam. Many poor translations offer little more than the bias and ignorance of the translator. But it's imperative to remember that any translation is at best an approximation, and it can be very dangerous to make sweeping judgments based on translated verses, especially in isolation.
6. Not all Muslims are Arabs; not all Arabs are Muslims. There seems to be widespread confusion about this. I suppose that, on some level, it's understandable: the Qur'an was revealed to an Arab speaker in Arabia, and two of Islam's holiest sites (the Holy Mosque in Makkah and the Prophet's Mosque in Madinah) are in what is now Saudi Arabia. But Arab people live in many countries, not just Saudi Arabia, and subscribe to many different religions, not just Islam: Christianity, Judaism, and Druze among them. The most populous Muslim country in the world is not even an Arab country: it's Indonesia. Only about twelve percent of the world's Muslims are Arabs. Muslims are nationals of many countries, from India to Sweden to Australia. Anyone who wants to can convert to Islam, and it's actually only a minority of Muslims who are also of Arab heritage. Also, not all Arab customs are Muslim. All Muslims do not speak Arabic, although prayers are to be said in Arabic, and Muslims are encouraged to learn to read Arabic so that they can understand the Qur'an. And while I would really, really like to believe this doesn't even need to be said, recent events have proved me wrong: not everyone with brown skin or wearing a turban is a Muslim or an Arab.
7. Culture is not religion. So much of the oppression and misogyny (female illiteracy, "honor" killing, female genital mutilation, forced marriages, physical abuse, etc.) we hear about in quasi- and pseudo-Islamic countries such as Pakistan, Saudi Arabia, and Iran stems from patriarchal cultural customs and baggage and not from Islam, although it's always "justified" sixty ways to Sunday with supposed religious dictates and self-serving interpretations of ******ure.
If any of these countries actually thoroughly implemented Islam as intended and honored the spirit as well as the letter of the "law," women, for example, would not only have far more rights and freedoms than they currently do in any of these countries, but the behavior of men and the actions of governments would have to change so radically that you would probably not recognize these countries at all. Islamic concepts and requirements are that different from how these countries currently operate.
8. Islam is not a monolith. It is a large, widespread, rich, and complex religion, with an extremely intricate and sometimes enigmatic ******ure, and an estimated 1.2 billion followers worldwide. There is overwhelming diversity within the Islamic world, beginning with the major Islamic subgroups: Sunni Muslims (accounting for around 85-90% of Muslims), Shi'ite Muslims, Sufis, Ismailis, and other small splinter groups. Within these groups there are schools of legal thought; there are four major ones within Sunni Islam alone. Muslims might be born into the religion or convert to it, and this contributes to the diversity within its adherents. It's absolutely essential not to see any one Muslim, genuine or otherwise, as representative of all Muslims.
The very diversity of Muslims worldwide is one reason the annual pilgrimage (hajj) to Makkah, the birthplace of Islam, is so compelling: every year for over fourteen hundred years, millions of Muslims have united for a few days, putting aside all differences of race, ethnic background, class, gender and language, to participate in a ritual established by the Prophet Muhammad.
9. Jihad does not mean "holy war." This has to be one of the most damaging, most persistent myths about Islam. The Western media have helped perpetuate this, but there are plenty of benighted Muslims who insist on misapprehending and incorrectly using this term. Jihad, (which comes from the Arabic root word jahada, meaning "to toil, to exert oneself, to strive for a better way of life") is correctly translated as "struggle" or "endeavour," and can easily apply to such things as a student working to earn a medical degree or a group of people raising money to build a mosque. It can apply to the struggle to control one's temper, or to learn to read and write. Part of my husband's jihad as a Muslim is the effort it takes for him to get up in time to offer the first prayers of the day, which occur before dawn. It encompasses the idea of struggling or fighting for good or against evil, but that does not necessarily mean with violence, and it certainly does not mean that any crackpot claiming to be Muslim and waving a Qur'an around can decide who is good and who is evil, and start killing people.
There are certain extreme circumstances under which the notion of jihad might encompass aggression or armed conflict, but these are only to be engaged in as a last resort, when all legal, political, economic, social, and diplomatic attempts to defend Muslims and their right to worship, or to combat other severe oppression (and not only against Muslims), have failed. Any kind of military action is, at best, a subset of the concept of jihad. In fact, there is a well-known Islamic saying indicating that any kind of military conflict is the "minor jihad"; the "major jihad" is the struggle to control and improve oneself. Some of the passages in the Qur'an describing battle and aggression (the passages militants often quote out of context to support their agendas) are narrating actual historical events, not advising them as a course of action or a religious duty. They are also offset by many other passages enjoining peace, mercy, goodness, tolerance, patience, forgiveness, compassion, restrictions in warfare, etc. It seems the bin Ladens and "Muslim" militants of the world just haven't gotten to those parts of the Qur'an yet.
10. Islam does not promote, sponsor, condone or encourage terrorism or murder. The smear campaign against Islam (during the twentieth century in particular) has been extremely thorough and successful