The ancient title of the Colosseum, known as Amphitheatrum Flavium (Flavian Amphitheater), is attributed to its construction during the rule of the Flavian dynasty, after the reign of Emperor Nero. In a peculiar way, this name was not limited to the Colosseum, since Vespasian and Titus, the architects of this majestic amphitheater, also erected another enclosure of similar characteristics in the town of Puteoli (today known as Pozzuoli), to which they gave the same name. Although the epithet "Flavian Amphitheater" is still in use today, the colossal building is universally identified as the Colosseum.

In ancient times, the Romans may have unofficially referred to the Colosseum as the "Amphitheatrum Caesareum," although this designation may have had a more poetic than practical connotation.

The currently recognized appellation, "Colosseum," began to gain notoriety beginning in the eighth century and is presumed to have originated due to the presence of a monumental statue of Emperor Nero, popularly known as the "Colossus" (Colossus), which stood in the vicinity of the building. It is believed that the statue was taken down at some point to recycle its bronze, and only its pedestal has survived, located between the amphitheater and the temple of Venus and Rome.

The original Latin name, Colosseum, gradually evolved into Coliseum in the Middle Ages, giving rise to the English term "Colosseum", which eventually became more popular than "Flavian Amphitheater". Over time, this term also became a reference for large buildings intended for entertainment, including large-scale theaters and, in general, any other impressive building intended for spectacle.