There doesn't seem to be a firm definition of "cult" but it is easy to find information. Here is one paragraph from a website that describes some cults.
Sociological, psychological, and journalistic observations sometimes show us the human dynamics that frequently result from a cult belief system, but they are not sufficient Christian foundations for determining a groups status as a cult. For example, a cult's unique doctrines can lead to an exclusivism and separateness from other religious groups. A cult's belief that the Bible's revelation is superceded by the current revelations of the cult leader may result in followers surrendering their thinking and decision making abilities to the cult leader. And the more aberrant a cult's beliefs and practices, the more likely it is to be characterized as bizarre.