There was some discussion on this earlier, so here are the different forms of religion:
New Religious Movement: A really keen interest to us when we look at different kinds of societies. Many sociologists of religion will argue that our societies in Canada are not less religious than they used to be a couple of generations ago, but different in the focus of their religious beliefs. Old traditions are crumbling, but new ones are coming to replace them.
A New Religious Movement (NRM) is defined as an informal group without defined structure. They come about for a variety of reasons, most often emerging around around an authoritatian and charismatic leaders. In the United States, Sarah Palin is clearly very religious (though the Tea Party movement is largely political, though possibly religious), but also a charismatic leader. People follow her, despite the lack of logic and rationality, neither of which play a role, which is what is interesting to social sciences. When you're a religious organization, it doesn't have to make sense. If it's your Faith, that's all you need.
NRMs isolate members and suppress rational thought. Some of the debate in the US over their last political elections was not rational in any way. NRMs usually disband once the leader dies or disappears, as they are effectively what held it together.
Sect: Small religious body with exclusive or voluntary membership that is aloof or hostile to the larger society. They go along with the fundamental teachings, but are unhappy with the direction things are going, so will go and form their own groups, sometimes growing so disconnected with the rest of society that they don't want much to do with it. They are formed when a group breaks from a larger religious group.
Church: If you drive around Waterloo right now, you will see a bunch of churches being built or newly built. Religion is certainly a growing enterprise. A Church is defined as an institution that brings together a moral community of believers in formal worship and integrates itself within the larger secular world. They are most prevalent in societies with a high degree of religious pluralism. A pluralistic society is a society where all sorts of viewpoints are co-existing and participating in society. Canada has a tremendous amount of religious pluralism. Most religions are represented by somebody in this country.
Ecclesia: a state religion, which many nations have. They have ascribed membership. When a country attaches itself and its identity to a particular religion, this is what we call it. Examples include the Catholic Church in Italy, Islam in Iran/Saudi Arabia/Syria/Others, Lutheran Church of Sweden, and Anglican Church of England (of which the Queen is the Head).
Denomination: socially accepted religious body that has bureaucratic characteristics, similar to those of the church. They are usually IN a church, sort of a sub-group within the church. A way to think about this is that within Christianity, there is Protestantism, but in Protestantism there are Uniteds, Anglicans, Presbyterians, etc., who do things in a slightly different way. They are self-governing and seen as a midpoint between church and sect. Dominations usually get along with each other but don't necessarily want to have religious ceremonies together.
Source: These are notes I took in Sociology.
That all said, Scientology is, indeed, a Church, and not a cult or NRM. No matter how much you hate them.