1. Classical Arabic is the oldest type of Arabic that is studied widely. It is the language of the al-Qur'an and texts from the classical age of the Islamic empire (including texts dealing with Qur'anic subjects), the Hadith (the record of the Prophet Muhammad's words and actions), Islamic law and theology, history, biography, geography, poetry, grammar, medicine, astronomy, and other sciences. Until a few decades ago, this was the type of Arabic most commonly taught in American Universities. Classical Arabic is still used today, but is restricted to religious and highly formal contexts.
2. Modern Standard Arabic or al-FuSHaa is a direct descendant of Classical Arabic and is now the language of elevated discourse or correspondence, contemporary literature, and the mass media (whether newspaper, radio, television, or the internet). Modern Standard Arabic is a formal, mainly written language that is not used for daily-life communications. There are no native speakers of Modern Standard Arabic, but the vast majority of the educated in the Arab world learn Modern Standard Arabic through formal schooling. Although Arabs not educated formally cannot produce Modern Standard Arabic, many can comprehend it because of the considerable overlap between the different varieties of Arabic. Modern Standard Arabic remains largely uniform throughout the Arab world.
3. Colloquial Arabic or 'aammiyya, refers to the regional dialects used in everyday discourse and popular culture media (music, movies, etc.) There are numerous dialects in the Arab world that vary along geographical, socio-economic, and religious lines. Arabs from one region can generally understand dialects from other regions, depending on proximity, exposure to other Arab dialects, education and command of Modern Standard Arabic.