Sufism is One of the Most Dynamic and Interesting Dimensions of Islamic religious and cultural expression. It is an umbrella term for a variety of philosophical, social, and literary phenomena occurring within the Islamic world. In its narrowest sense, the term “Sufism” refers to a number of schools of Islamic mystical philosophy and theology, to the phenomenon of religious orders and guilds (tarīqāt) that have exerted considerable influence over the development of Islamic politics and society, and to the varied expressions of popular piety and devotion to shrines found throughout the Islamic world. In a wider sense, Sufism is often seen as the spiritual muse behind much of pre-modern verse in the Islamic world, the idiom of much of popular Islamic piety, the primary social arena open to women's religious participation, and a major force in the conversion of people to Islam in Africa and Asia. The Sufi orders served as educational institutions that fostered not only the religious sciences but also music and decorative arts. Their leaders sometimes functioned as a challenge to the power of the juridic and theological establishment.