A guide to its key concepts
The Origins of Islam
The story of Islam begins with an orphan, Muhammad ibn Abdullah, raised in the harsh desert of what is now Saudi Arabia. Trained as a merchant, he experienced his first divine revelation at the age of 40 on a mountainside near the city of Mecca. The angel Gabriel appeared to him, uttering the command "Iqra" - "Recite!" It was the first of a series of revelations that would last until his death. Years later they were collected and written down to form the Qur'an (Koran), a book that would become the foundation of an entire religion and civilisation.
At the beginning Muhammad and his followers faced persecution, forcing them to find refuge in the city of Medina. Soon, their fortunes turned. An eight-year war led to victory over the polytheistic Meccans, and by the time of Muhammad's death, two years later, most of Arabia's tribes were united under the new monotheistic faith. Within a century, Islam would spread as far west as Spain and as far east as Afghanistan.
Allah
The Arabic name for "God"; the word refers to the same God worshipped by Christians and Jews.
Caliph
The Prophet Muhammad's successors were known as caliphs. The first four caliphs, beginning with Abu Bakr, are known as the "rightly guided" caliphs. Shia Muslims believe that the fourth caliph, Muhammad's cousin and son-in-law Ali should have been the first caliph.
Hilal
The Arabic word for crescent moon, it has become a symbol of Islam because of its association with sighting of the new moon at the beginning and end of the holy month of Ramadan. The crescent is often incorporated in the design of the minaret, the tower in a mosque from which the call to prayer is given. It also features in the flag design of several Muslim countries.
Islam
Derived from an Arabic root meaning "peace", in this form the word means "submission" or "surrender" to the will of God.
Islamic calendar
The first year of the Muslim calendar is 622 AD, the year of Muhammad's flight to Medina. The Islamic calendar consists of 12 lunar months. Common years last 354 days, and leap years last 355 days.
Jihad
An Arabic word meaning "to struggle". This is usually taken to mean striving to live in accordance with God's commands. But it can also apply to fighting to defend Muslims. The latter jihad, however, is supposed to be fought according to strict rules of war.
Kaaba
The most sacred shrine of Islam, it is a cube-shaped stone structure in the centre of the great mosque in Mecca. According to tradition, the Kaaba was built by Abraham and his son Ishmael.
Mecca
Islam's most sacred city, located in what is now western Saudi Arabia. According to Islamic tradition, the city was founded by Adam. Mecca is the birthplace of Muhammad and the site of the Kaaba.
Medina
Also located in western Saudi Arabia, Medina is Islam's second holiest site. Muhammad migrated to Medina in 622 after being persecuted in Mecca. It is also the site of Muhammad's tomb.
Mosque
The Arabic word for mosque is masjid, meaning "place of prostration" before God. Muhammad built the first mosque in Medina.
Muslim
In Arabic, "one who submits or surrenders to God"; a follower of Islam.
Pillars of Islam
Five observances that form the basis for being a Muslim: the shahada (profession of faith), salat (the five daily prayers), zakat (alms giving), sawm (fasting during the month of Ramadan) and hajj (making the pilgrimage to Mecca).
The hajj takes place during the 12th lunar month of the Islamic calendar. The pilgrimage that takes place at other times is called the umra. About two million Muslims carry out the hajj each year.
Qur'an
The holy book of Islam, revealed to the Prophet Muhammad over a period of 23 years. The word Qur'an means "recitation". Muslims consider it to be the direct word of God. It consists of 114 surahs, or chapters, each divided into ayat, or verses.
The Qur'an is the primary source of Islamic law, or Shariah, followed by hadith (teachings and sayings attributed to Muhammad) and the sunna (the habits and practices of Muhammad's life).
Shia
As supporters of Ali, the fourth caliph, the Shias eventually became a distinct Muslim group. The largest Shia Muslim sect is the "Twelver Shia", named after the first 12 leaders (or imams) of Shia Muslims. Twelver Shia believe that the descendants of Ali, Muhammad's cousin and son-in-law, were the legitimate leaders of Islam.
Shias believe the last imam is in hiding, and they await his return.
Shias are the majority in Iran, and many can be found in Iraq, Lebanon, Syria and Pakistan.
Sunni
The majority of the world's Muslims follow Sunni Islam. Unlike Shia Muslims, Sunni adherents believe Islamic leadership should come from the consensus of the community, rather than religious and political authorities.
Umma
A word used to describe the worldwide community of Muslims.