Shi‘a ("followers" or "partisans") as an Islamic term traces its etymology to the very first century of Islam.
The singular/adjective form of Shi‘ah (Arabic: شيعة) is Shi‘i (Arabic: شيعي). The apostrophe frequently used (e.g. Shi'a) is technically incorrect, since the Arabic letter is the ayin (ع), standardly represented with a grave accent (`), left half-circle (ʿ), or turned comma (‘). The apostrophe represents the hamza, which has a noted difference in pronunciation. The final Arabic letter is the ta' marbuta, which also causes difficulty in transliteration. It is often pronounced as a soft /h/ (e.g. Shi‘ah), but in a construct state, and in more classical Arabic, it is pronounced as a /t/ (e.g. Shi‘at ‘Ali). The ta' marbuta is frequently dropped in transliteration (e.g. Shia).
Due to the complexities of Arabic, there are approximately 30 possible transliterations of شيعة. For technical accuracy Shi‘ah is the preferred form. Using the Arabic chat alphabet, the transliteration is Shi3a.
Shia (/ˈʃiːə/; Arabic: شيعة Shīʿah), an abbreviation of Shīʻatu ʻAlī (شيعة علي, "followers of Ali"), is a branch of Islam which holds that the Islamic prophet Muhammad's proper successor as Caliph was his son-in-law and cousin Ali ibn Abi Talib. Shia Islam primarily contrasts with Sunni Islam, whose adherents believe that Muhammad's father-in-law Abu Bakr was his proper successor.
Adherents of Shia Islam are called Shias or the Shi'a as a collective or Shi'i individually. Shia Islam is the second-largest branch of Islam: in 2009, Shia Muslims constituted 10–13% of the world's Muslim population.Twelver Shia (Ithnā'ashariyyah) is the largest branch of Shia Islam. In 2012 it was estimated that perhaps 85 percent of Shias were Twelvers.
Shia Islam is based on the Quran and the message of the Islamic prophet Muhammad attested in hadith recorded by the Shia, and certain books deemed sacred to the Shia (Nahj al-Balagha). Shia consider Ali to have been divinely appointed as the successor to Muhammad, and as the first Imam. The Shia also extend this "Imami" doctrine to Muhammad's family, the Ahl al-Bayt ("the People of the House"), and certain individuals among his descendants, known as Imams, who they believe possess special spiritual and political authority over the community, infallibility, and other divinely-ordained traits. Although there are myriad Shia subsects, modern Shia Islam has been divided into three main groupings: Twelvers, Ismailis and Zaidis, with Twelver Shia being the largest and most influential group among Shia.