This definition is from the auther of a new novel "China Lake" by Meg Gardiner
Amazon.com: What’s the difference between a cult and religion in your opinion?
Gardiner: A religion is a system of beliefs about the true nature of existence and humanity’s connection to the divine--to a supernatural reality beyond what we can see with our eyes. And it’s a community that shares convictions about what people must do to bring themselves closer to God. (Or bliss, or enlightenment.) A cult, to vastly simplify, is a group that takes religion to extremes. It’s fanatical, manipulative, and in the end, destructive. Cults demand total commitment. They often have charismatic leaders who require absolute subservience from followers. And they’re coercive. They tear members away from their previous lives to isolate them from the wicked, tempting world. They may force followers to break contact with family and friends who are “unsaved” or “infidels.”
Cults divide the world into Good--them--and Evil--the rest of us. To those in their blessed little band they offer love, salvation, and paradise. They promise members a unique role at the center of great cosmic events. Some promise followers a front row seat for Armageddon. Sometimes they just take people’s money and hollow out their spirits. But cults feed on us-versus-them thinking. They may believe they’re embattled, and nurture a raging sense of grievance. This makes them prone to conspiracy theories. They can become paranoid, and start to believe that great forces are not just persecuting them, but massing to strike. And at that point they can spiral into violence, self-destruction, or terrorism.