A cult is a group of people who have more drastic religious ideas. For example a statist cult involves sacrifice and many other things which most people do not enjoy. Basically religion is a more developped and practical thing while a cult is not.
A cult is marked by unquestioned (or "unquestionable" by implication) authority of its leader(s). It typically involves the severing of existing relationships (even immediate family and close friends) in order to join and involves the restructuring of ones whole social life. It's beliefs are in reality subordinate to the allegiance to its leader(s). Probably the most negative element of a cult is the manipulation used to gain adherents and to keep them (psychological slavery). Any "healthy" religion can certainly become a cult, even if its just within certain circles of a given religion, but a religion is understood to be void of cult qualities. Usually a cult uses a religion's set of beliefs as a front (unconsciously even) for the dark control it actually has. It's interesting that the word "cult" originally and still is used by cultural anthropologists to describe specific religions of the past and is the root word for the word "culture/cultural". Perhaps we all manipulated and controlled by out own "cult-rue"....oh, boy!!
They are very similar but a 'religion' is focused on a Higher Power of some sort usually, and not specifically on the leader alone whereas a cult is solely focused on the leader as an all powerful 'god' figure. In fact most cults are started by megalomaniacal people (almost always men) with a desperate need to be all powerful and totally in control of every aspect of those around him. Sometimes these men use Gods name to hide behind and sometimes they claim empowerment by aliens but its really always only about themselves. Religions present members with beliefs and ruled but members are still free to leave if they wish and form their own opinions. Cults are into brainwashing and mind control. Members are only allowed to believe exactly what the leader teaches and have no freedom of thought or freedom of control to leave. Cults also tend to be very secretive and institute strict use of physical and mental punisments for straying from the prodigious and detailed rules. Some religions exhibit borderline cultish qualities -- EXAMPLES: the Amish (strict rules, shunning, banishment) Catholics (the pope, viewing the pope as the embodiment of God on earth, strict rules, excommunication of those who dont follow their rules) Islam (pretty obvious, esp in their control and subjugation of women, strict rules and death for anyone who violates or disagrees with those rules)
When we hear the word "cult," we often think of a group that worships Satan, sacrifices animals, or takes part in evil, bizarre, and pagan rituals. However, in reality, most cults appear much more innocent. The specific Christian definition of a cult is "a religious group that denies one or more of the fundamentals of biblical truth." In simpler terms, a cult is a group that teaches something that will cause a person to remain unsaved if he/she believes it. As distinct from a religion, a cult is a group that claims to be part of the religion, yet denies essential truth(s) of that religion. A Christian cult is a group that denies one or more of the fundamental truths of Christianity, while still claiming to be Christian. The two most common teachings of cults are that Jesus was not God and that salvation is not by faith alone. A denial of the deity of Christ results in Jesus death not being a sufficient payment for our sins. A denial of salvation by faith alone results in salvation being achieved by our own works, something the Bible vehemently and consistently denies. http://www.gotquestions.org/cult-definition.html