A cult or heretic was an individual or group of individuals who possessed radical beliefs, usually religious, that were outside of the mainstream. They were known to possess tight control over their followers' minds, eliminating all forms of dissent from within themselves.
A small cult was formed on Bajor that worshiped the Pah-wraiths, believing them to be the true gods of Bajor. The Pah-wraith cult was considered a joke until late 2374, when Dukat released a Pah-wraith into the Bajoran wormhole, collapsing it, and starting a celestial war. A young member of the cult tried to assassinate Captain Benjamin Sisko on Earth several months later. (DS9: "Image in the Sand", "Covenant")