1.A high-ranking Shiite religious authority regarded as worthy of imitation in matters of religious law and interpretation.
2.Used as a title for such a leader.
lit. Sign of God
Ayatollah is a high rank given to major Shi'a clerics. The word means 'sign of God', and those who carry the title are experts in Islamic studies such as jurisprudence, ethics, philosophy and mysticism, and usually teach in schools (hawza) of Islamic sciences. The next lower clerical rank is Hojat-ol-Islam ("authority on Islam").
The rank is granted by consensus, rather than ceremonially: an esteemed religious scholar who has earned the respect and admiration of his teachers for his knowledge and behavior after completing his Hawza studies. By then he would be able to issue his own edicts from the sources of religious laws (Quran, Sunna, Ijma'e, Aql). Most of the time this is attested by an issued certificate from his teachers. This Ayatollah then can teach in religious Hawza according to his speciality and can act as a reference for their religious questions and as a judge.
Only a few of the most important Ayatollahs are accorded the rank of Grand Ayatollah (ayat ullahi 'l-`udhma, "great sign of God"), or Marja al-taqlid ("reference for emulation"). This usually happens when the followers of one of the ayatollahs refer to him in many situations and ask him to publish his Jurdistic book in which he answers the vast majority of daily Muslim affairs. The book is called Risalah 'Ilmiyah which is usually a reinvention of the book Al-Urwat-ulWuthqah according to their knowledge of the most authentic Islamic sources and the current life.
There is usually one Grand Ayatollah in Iraq that heads the Hawza (curently Ali al-Sistani). There are more in Iran and wherever Shi'a exist.
There are more than 20 living, the most famous of them are: Grand Ayatollahs worldwide: Jawad Tabrizi, Ali Khamenei, Ali al-Sistani, Kazem al-Haeri, Muhammad Fazel Lankarani, Ali Montazeri, Mohammad Hussein Fadlullah and Sadiq Hussaini Shirazi.
When Westerners say 'the Ayatollah', they usually mean Ayatollah Ruhollah Khomeini, who brought the word into the international limelight during the 1979 Iranian Revolution; a possible secondary meaning would be the term's use to indicate the serving Supreme Leader of Iran.