A cult is any religion that venerates a man, false deity, elementals, heavenly beings, etc; basically anything that is not the true God.
ie: cults of humankind (Cult of the DPRK Kim Dynasty, Ancestor worship, Imperial cults, etc.)
cults of the doctrines of man (Lutheranism, Calvinism, Wesleyanism, Judaism, etc.)
cults of daemons (Hellenism, Wicca, Hinduism, etc.)
cults of elementals/earthy beings (Fire worship, Earth worship, Animal worship, etc.)
cults of heavenly beings (Astrology, Sun worship, Angel worship, Moon cults, etc.)
cults of idols or inanimate beings (Statue worship, Cargo cults, Money worship, etc.)
Typically the attributes of the above will overlap. For example Islam is mentioned much, they perform rituals to an idol (the black rock of Mecca) and venerate the doctrines of Mahomet whom was also possibly inspired by daemons. Or in Hinduism being a very broad term for smaller cults of daemons, idols, ancestor worship, and elemental worship, etc.