Religion
Nearly every citizen of Bahrain is a Muslim as over 80% of the country prescribes to this religion. Among the other 20%, about half are Christian and half adhere to other religions. There are numerous non-citizens in the country as well; among these people numerous religions are common, including Christianity and Hinduism.
Islam (the name of the religion, whose followers are called Muslims) is a monotheistic religion, whose holy book is called the Qur'an. The Qur'an is believed to be the word of God spoken through the prophet Muhammad from 609-632 CE (Common Era is preferred over AD (Anno Domini or "year of the Lord") since the Islamic world doesn't believe Jesus was the messiah). Islam believes Muhammad was the last prophet sent to earth by God, the last in a long line of prophets, which includes Moses, Abraham, and Jesus among others.
Muslims follow five pillars of their faith: testimony, prayer, alms-giving, fasting, and pilgrimage. These pillars, and other tenants of their faith, can give great structure to their lives as some foods, like pork, are forbidden and every Muslim is expected to pray five times a day. However, the level of participation in each of these pillars and to what degree Islam influences an individual's life varies from person to person and community to community. Generally speaking, Bahrain is fairly liberal in how they practice Islam.
Most Muslims are Sunni, which is the branch of Islam that closely follows the teachings of Muhammad and accepts Abu Bakr as the first Caliph (a ruler of an Islamic community); the Sunni Muslims are sometimes referred to Orthodox. Shia Muslims believe only God can chose who heads the Islamic community and believed it was Ali, Muhammad's son-in-law who was first chosen; Ali became the first Imam (according to Shia Muslims, this term only refers to the leaders of the faith, to Sunni Muslims Imam is often times used in reference to the prayer leader in mosques).