A circus was the site of performances by various acts. The travelling nature of circuses made tents a popular choice for their infrastructure.
The acts often included conjurers, acrobats, clowns and performances by animals, such as elephants.
The Third Doctor visited Luigi Rossini's International Circus after learning of the Master's activity there. (TV: Terror of the Autons)
When the Twelfth Doctor and Clara Oswald visited Blackpool in 2089, they encountered wild giraffes, parrots and lions which had escaped from the circus. (PROSE: All the Empty Towers)
The Psychic Circus was taken over by the Gods of Ragnarok on Segonax. (TV: The Greatest Show in the Galaxy)