Which of the following terms defines a formal Roman marriage ceremony?

The term that defines a formal Roman marriage ceremony is indeed confarreatio. This was a highly religious and formal type of marriage among the ancient Romans, primarily reserved for patricians. The ceremony involved various rituals, including the sharing of a sacred cake made from spelt (far), which was a key aspect of its namesake.

Confarreatio established a distinct legal status and was significant in reinforcing social and familial alliances among the patrician class. It required the presence of ten witnesses and a flamen Dialis (a priest), highlighting its formal and sacred nature. This type of marriage conferred specific rights and privileges, making it not only a personal union but also a significant social contract within Roman society.

The other options represent different aspects of Roman relationship dynamics. Usus refers to a less formal union based on cohabitation, while coēmptiō pertains to a form of marriage that involved a form of sale and was often used among plebeians. Contubernium, on the other hand, defined a cohabitation arrangement that did not constitute a legal marriage. Thus, confarreatio is uniquely positioned as the formal and religiously sanctioned marriage ceremony.