Asidism, sometimes spelled chassidism, and also known as hasidic judaism (ashkenazi hebrew חסידות ḥăsīdus, [χasiˈdus]; originally, "piety"), is a religious movement within judaism that arose as a spiritual revival movement in the territory of contemporary western ukraine during the 18th century, and spread rapidly throughout eastern europe. today, most of those affiliated with the movement, known as hassidim, reside in israel and in the united states.