The word "cult" gets bandied about quite a bit, but is there an official definition or some kind of formula which can be used to consistently identify whether a group is a cult or not? Baring an absolute standard, what are the various usages and who tends to use each possible meaning?

In particular, I am interested in focusing on the sense in which the word is able to adapt to apply to both one man whack jobs such as [David Koresh](http://en.wikipedia.org/wiki/David_Koresh) as well as larger stable groups such as [Mormons](http://en.wikipedia.org/wiki/Mormonism) or [Jehovah Witnesses](http://en.wikipedia.org/wiki/Jehovah%27s_Witnesses) but not for the major traditions such as [Catholics](http://en.wikipedia.org/wiki/Catholic_Church) or [Protestants](http://en.wikipedia.org/wiki/Protestantism)? What definition is used in Christian circles that makes this usages make sense?