A language spoken by over 250 million people from Syria to Iraq to Mauritania and understood, to varying degrees, by Muslims across the world.
Standard Arabic ('fusHa') is a modernized form of classical Arabic and is used as a lingua franca in the Arab world, primarily in written form. It is also used in newscasts, official and academic lectures and in religious situations.
Each region (each town in some areas) has its own colloquial version of Arabic composed of standard Arabic and various loan words used with a simplified (usually), flexible grammar. This diglossia is pronounced in certain regions to the extent that many North African dialects (Moroccan, Algerian, Hassania -- from Mauritania) are nearly unintelligble to Arabs from Lebanon and Yemen. Egyptian Arabic is widely understood due to Cairo's status as the media center of the Arab world. This is true of the Levantine (Syria and Lebanon) dialect to a lesser extent.