A Daedric Cult is a group of people associated with the worship of the Daedric Princes.
Most people not associated with Daedric cults view them as blood-drinking maniacs. Because of this, worshipers lead a solitary life. In reality, each cult acts according to the prince they worship. The worshipers of Sanguine, for example, engage in pleasurable acts, such as drinking, partying and sex, while the worshipers of Sheogorath will be mad, talking nonsensically, and not wearing much clothing, or followers of Hircine may be obsessed with hunting or see anyone who is infected with Lycanthropy as a god.
The most infamous of the Daedric Cults is the Mythic Dawn, which, during the Oblivion Crisis, assassinated Uriel Septim VII and all of his sons save for Martin Septim, and assisted Mehrunes Dagon with his invasion of Tamriel.