Sufism ( aṣ-ṣūfiyya), also known as Tasawwuf ( at-taṣawwuf), is a mystic body of religious practice, found mainly within Sunni Islam but also within Shia Islam, which is characterized by a focus on Islamic spirituality, ritualism, asceticism and esotericism. It has been variously defined as "Islamic mysticism", "the mystical expression of Islamic faith", "the inward dimension of Islam", "the phenomenon of mysticism within Islam", the "main manifestation and the most important and central crystallization" of mystical practice in Islam, and "the interiorization and intensification of Islamic faith and practice". Practitioners of Sufism are referred to as "Sufis" (from , ), and historically typically belonged to "orders" known as (pl. ) – congregations formed around a grand who would be the last in a chain of successive teachers linking back to Muhammad. Sufism emerged early on in Islamic history, partly as a reaction against the worldliness of the early Umayyad Caliphate (661–750) and mainly under the tutelage of Hasan Al-Basri. Although Sufis were opposed to dry legalism, they strictly observed Islamic law and belonged to various schools of Islamic jurisprudence and theology. Although the overwhelming majority of Sufis, both pre-modern and modern, remain adherents of Sunni Islam, certain strands of Sufi thought transferred over to the ambits of Shia Islam during the late medieval period. This particularly happened after the Safavid conversion of Iran under the concept of Irfan. Important focuses of Sufi worship include , the practice of remembrance of God. Sufis also played an important role in spreading Islam through their missionary and educational activities. Despite a relative decline of Sufi orders in the modern era and attacks from revivalist Islamic movement (such as the Salafis and Wahhabis), Sufism has continued to play an important role in the Islamic world, especially in the neo-traditionalist strand of Sunni Islam. It has also influenced various forms of spirituality in the West and generated lots of academic interest. However, some recent scholarship has challenged the Western understanding of Sufism as orientalist in nature. Definitions The Arabic word tasawwuf (), generally translated as Sufism, is commonly defined by Western authors as Islamic mysticism. The Arabic term Sufi has been used in Islamic literature with a wide range of meanings, by both proponents and opponents of Sufism. Classical Sufi texts, which stressed certain teachings and practices of the Quran and the sunnah (exemplary teachings and practices of the Islamic prophet Muhammad), gave definitions of