The term `cult' is is a term of disparagement and is usually used to refer to unconventional religious groups, though the term is sometimes used to refer to non-religious groups which appear to share significant features with religious cults. For example, there are some who refer to Amway and est as cults, but I think the terms is best reserved for groups such as the Rev. Sun Myung Moon's Unification Church, the Hare Krishnas and the group which followed the Rev. Jim Jones to Guyana where more than 900 of them joined in a mass murder/suicide ritual.
Three ideas seems essential to the concept of a cult. One is thinking in terms of us/them with total alienation from them. The second is the intense indoctrination techniques used to recruit and hold members. And the third is the charismatic cult leader. Cultism usually involves some sort of belief that outside the cult all is evil; inside the cult is the special path to salvation through the cult leader and his teachings. The indoctrination techniques include
1) Subjection to stress and fatigue
2) Social disruption, isolation and pressure
3) Self criticism and humiliation
4) Fear, anxiety and paranoia
5) Control of information
6) Escalating commitment
7) Use of auto-hypnosis to induce 'peak' experiences
[Kevin Crawley]
Of course, there is a positive side to cultism. One gets love, a sense of belonging, of being special, of being protected, of being free from the evils of the world, of being on the path to eternal salvation, of having power. If the cult did not satisfy needs that life outside the cult failed to satisfy, cults would not exist.
See related entries on channeling, dianetics, mind-control, and Rama.
further reading
Persuasion Techniques Used by Cults (Singer & Lalich)
The "Not Me" Myth: Orwell and the Mind by Margaret Thaler Singer Ph.D.
"Cults, Anti-Cultists, and the Cult of Intelligence," by Daniel Brandt
The Ontario Centre for Religious Tolerance page on Cults
Testimonies of scientologists and critics
Scientology: The Thriving Cult of Greed and Power
The Kingdom of Cults, Walter Martin, revised and expanded (Minneapolis: Bethany House, 1985).
The New Age Cult, Walter Martin (Minneapolis: Bethany House, 1989).