One basic thing I have been told is that a cult is a group of people who deny that Jesus is "God". And they claim the Bible but do not go by what it says. And they control their members. They might make some person or thing the "enemy" and keep a lot of attention on that enemy and make a project of criticizing that enemy, and this keeps attention away from how their own leader or leadership is wrong.
Of course, by the way, any of us can do this, our own selves > I mean, how we can be so busy pointing the finger at someone else so we and others don't notice how we ourselves are wrong.
Also, I see how a cult can have very different things and standards and requirements so they can say, only we have this and this is essential and so you need to join us.
But a Christian denomination can do this, too > having more or less unique practices and beliefs and saying they are so important and no one or not everyone else has them and so you need to join that denomination. So a denomination can be cultic.