The difference is scale. The larger they are, the longer they last, the more people they collect. More people means greater sociocultural presence which means more widespread acceptability even with non-believers. More people also means more money and other resources which means more power, the capacity to bend the society in which they exist. The larger “religions” label the smaller religions as “cults” as a form of basic anticompetitive practice.

cult n. - a small, unpopular religion.

religion n. - a large, popular cult.

They’re the same picture!

PR

edit: no, that’s mean. Real answer, how much they control the lives of their followers. example here

From what I understand, those who research religion prefer the term “high-control group” to describe what are colloquially known as “cults.” That’s partly due to people calling anything they don’t like a cult.

Picture two Christian denominations. One only asks its members to show up to church when they like, donate to keep the place running, and express Christ’s love to each other in whatever way they see fit without placing unnecessary burdens on them. The other demands, under pain of exile, that all members spend 40 hours per month on door-to-door evangelization regardless of social disposition, only receive theology that is dictated by one specific organization, tithe 20% of their income to that organization, only allows members to be friends with others in that particular denomination, and does not allow them to drink alcohol, smoke cigarettes, use any “hard” drugs, get tattoos, or receive blood transfusions.

Most people would probably agree that the second denomination is a cult/high-control group, but using that descriptor for the first denomination would dilute the term so much that it would basically become meaningless.

Not much nowadays.