And what's a cult? An unpopular religion.
Cults and religions differ, largely in how they propegate and gain members and resources.
Christianity is a religion. It is vastly unpopular in some places. Islam is also a religion. It's even more unpopular in other places. Neither could be called a cult. Scientology is called a cult because of it's business practices, more than its religious values. Likewise, most neo-Wiccan groups would be considered cults, rather than a religion, because of the lack of unity it suffers among it's own worshipers, but it's actually quite popular.
1.a particular system of religious worship, esp. with reference to its rites and ceremonies.
2.an instance of great veneration of a person, ideal, or thing, esp. as manifested by a body of admirers: the physical fitness cult.
3.the object of such devotion.
4.a group or sect bound together by veneration of the same thing, person, ideal, etc.
5.Sociology. a group having a sacred ideology and a set of rites centering around their sacred symbols.
6.a religion or sect considered to be false, unorthodox, or extremist, with members often living outside of conventional society under the direction of a charismatic leader.
7.the members of such a religion or sect.
8.any system for treating human sickness that originated by a person usually claiming to have sole insight into the nature of disease, and that employs methods regarded as unorthodox or unscientific.
1. a set of beliefs concerning the cause, nature, and purpose of the universe, esp. when considered as the creation of a superhuman agency or agencies, usually involving devotional and ritual observances, and often containing a moral code governing the conduct of human affairs.
2. a specific fundamental set of beliefs and practices generally agreed upon by a number of persons or sects: the Christian religion; the Buddhist religion.
3. the body of persons adhering to a particular set of beliefs and practices: a world council of religions.
4. the life or state of a monk, nun, etc.: to enter religion.
5. the practice of religious beliefs; ritual observance of faith.
6. something one believes in and follows devotedly; a point or matter of ethics or conscience: to make a religion of fighting prejudice.
7. religions, Archaic. religious rites.
8. Archaic. strict faithfulness; devotion: a religion to one's vow.
Note that almsot all religions can be defined as cults, but the inverse is not true.....