Over the past several weeks, the news has been filled with words and terms relating to Islam and Islamic culture. Here's a short guide.

Allah: The Arabic name for "God"; the word refers to the same God worshipped by Jews and Christians.

Caliph: The prophet Muhammad's successors were known as caliphs, and their empire was the caliphate. (Muhammad was a political as well as a religious leader.) The first four caliphs are known as the rashidun (the "rightly guided" caliphs). Sunni Muslims consider the rule of the rashidun to be the golden age of Islam. Shii Muslims believe that the fourth caliph, Ali, was usurped by the first three caliphs and that his descendants were the proper heirs to the caliphate. (One sect of Shiis set up a rival caliphate in Egypt in 983. It lasted nearly 200 years.) Umar, the second caliph, decreed that Jews and Christians should be removed from Arabia. (Such an expulsion was much rarer than the evictions of Jews and Muslims from medieval Christendom.) Since Umar's decree, Islam's holiest sites have been off-limits to non-Muslims.

Hajj: The pilgrimage to Mecca, which Muslims with the physical ability and financial means should perform at least once in their lives. It is one of the five pillars of Islam. The others are shahada (profession of faith), salat (prayer), zakat (alms giving), and sawm (fasting).The hajj takes place during the 12^th lunar month of the Islamic calendar and focuses on rituals around the Kaaba. A pilgrimage that takes place at another time is called the umra. Around 2 million Muslims carry out the hajj each year.

Islam: In Arabic, the word means "surrender" or "submission" to the will of God. Most Westerners think of Islam as one of the three major monotheistic world religions (the others being Judaism and Christianity). But the historian Bernard Lewis observes that "Islam" means both a religion (analogous to "Christianity") and the civilization that developed under that religion (analogous to "Christendom").

Islamic calendar: The first year of the Muslim calendar is 622 A.D., 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" or "to exhaust one's effort." The "effort" can mean preaching Islam and living virtuously in accordance with God's commands. But it can also apply to actual fighting to defend Muslims. Even military jihad, however, is supposed to be fought with respect for the rules of war.

Kaaba: The most sacred shrine of Islam, it is a cube-shaped stone structure in Mecca. Traditionally, Muslims believe the Kaaba was built by Abraham and his son Ismail. On the outside of one corner is the sacred Black Stone, kissed by pilgrims. The angel Gabriel gave the Black Stone to Abraham, according to one Islamic tradition; according to another, the stone was set in place by Adam.

Koran/Qu'ran: The holy book of Islam, recorded by the prophet Muhammad beginning in the year 610 A.D. Muslims consider it to be the word of God. Islam teaches that the Christian and Hebrew scriptures are also holy books, though they had become distorted over time. The Koran is the primary source of Islamic law, followed by hadith (teachings attributed to Muhammad that are not recorded in the Koran) and the sunna (the habits and practices of Muhammad's life). The word Koran means "recitation."

Mecca: Islam's most sacred city, located in what is now western Saudi Arabia. Mecca is the birthplace of Muhammad and the site of the Kaaba.