Modern Standard Arabic has developed out of Classical Arabic, the language of the Quran. During the era of the caliphate,Classical Arabic was the language used for all religious, cultural, administrative and scholarly purposes.
Modern Standard Arabic is the official Arabic language. It can be written and spoken, and there is no difference between the written and the spoken form.
In its written form, Modern Standard Arabic is the language of literature and the media. Books, newspapers, magazines, official documents, private and business correspondence, street signs and shop signs - all are written in Modern Standard Arabic.
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD. This includes both the literary language and varieties of Arabic spoken in a wide arc of territory stretching across the Middle East and North Africa. Some of the spoken varieties are mutually unintelligible, both written and orally, and the varieties as a whole constitute a sociolinguistic language. This means that on purely linguistic grounds they would likely be considered to constitute more than one language, but are commonly grouped together as a single language for political and/or ethnic reasons (see below). If considered multiple languages, it is unclear how many languages there would be, as the spoken varieties form a dialect chain with no clear boundaries. If Arabic is considered a single language, it perhaps is spoken by as many as 280 million first language speakers, making it one of the half dozen most populous languages in the world. If considered separate languages, the most-spoken variety would most likely be Egyptian Arabic, with 54 million native speakers still greater than any other Semitic language.