Sect is usually contrasted with churches or denominations.
Sects are thought to be small and inward-looking religious or spiritual groups which reject the values of the wider society. Examples of sects would be the Jehovah's Witnesses, Salvation Army, Christian Science.
These sects or groups typically begin with a charismatic leader who articulates a strong rejection of the compromises made with the secular world by other religions.
Over time, as sect leadership is routinized and members experience some upward mobility, there tends to be more acceptance of worldly matters and secular values.
Sects are differentiated by a number of doctrinal differences and have many beliefs and practices in common with the religion or party that they have broken off from. A denomination in contrast, is a large, well-established religious group.
From the Latin secta (from sequi to follow), meaning a
course of action or way of life. Sectarianism is sometimes defined in the sociology of
religion as a worldview that emphasizes the unique legitimacy of believers' creed and
practices and that heightens tension with the larger society by engaging in
boundary-maintaining practices. - McGuire, Meredith B. "Religion: the Social
Context" fifth edition (2002) ISBN 0-534-54126-7 page 338