No, a cult is any closed-off fanatical group that is deemed harmful to its members and sometimes to outsiders as well. The group who launched a sarin gas attack in Tokyo's metro, Aum Shinrikyo, was a cult. The Jonestown group was a cult. Scientology is often considered a cult, though this is less widely accepted (especially since Scientology is much larger).

No one considers Catholicism, or Protestantism, or Baptism cults. There may be specific communities that are cults that claim to be parts of these churches, but that doesn't mean that "pretty much any religion is a cult".