What is the term for a public square in a city, often used for gatherings and public affairs?

The term for a public square in a city that is often used for gatherings and public affairs is indeed "Forum." In ancient Roman cities, forums served as central gathering places where citizens could meet for various activities, including political discussions, commercial transactions, and social events. The forum was typically surrounded by important public buildings and temples, making it a hub of civic life.

In contrast, an arena refers to a space for sports and entertainment, such as gladiatorial games, while a basilica typically serves as a public building that may function as a court or a venue for other official gatherings, often distinguished by its architectural design. A coliseum is a large structure designed specifically for entertainment events, such as the famous Colosseum in Rome, and is not specifically a gathering space for civic matters. Thus, the correct identification of a forum encapsulates its role as an essential civic center in ancient urban life.