Cults are groups of people who believe in a version of how they think life should be lived and about what happens after death. It's not exactly classified as a religion but more as a society. Even the people in cults would deny that they were in a cult. Scientologists believe that they are part of a religion and not a cult. Cult is a broad term and frankly an opinion. It's a word that you would have to ask multiple people about before decided if it is a cult or not.
In the United States alone there are over 3,000 destructive cults. With that many cults, there are around 4 million active members involved. With around 325 million United States citizens, that means that 1.2% of our population is involved in a cult.