The language situation in the Arabic-speaking world
In the Arab world the language is in a state known as diglossia. This means that two varieties of Arabic are used under different conditions. The first is the ‘high’ variety of Arabic, close to Classical Arabic, which is known as Modern Standard Arabic (MSA). This is used in written media and in official speeches and lectures. The second is the ‘low’ variety of Arabic, known as Colloquial or Spoken Arabic, which is spoken and not usually written.
This situation is in flux, however: in recent years colloquial written Arabic has become prevalent on the Internet, and some literature does exist in colloquial Arabic, in Egyptian Arabic in particular.
Where Standard Arabic is largely the same throughout the Arabic world, colloquial variants vary immensely from country to country and from region to region. There is no strict separation between the ‘standard’ and ‘colloquial’ languages, but instead there is a sliding scale on which any language user constantly moves.
You may also be interested in