Which of the following terms describes a member of a religious order in the Roman Catholic faith?

The term that describes a member of a religious order in the Roman Catholic faith is "Sister" or "Nun." Members of religious orders typically take vows and live in a community, dedicating their lives to spiritual service, education, and helping the needy. Nuns, specifically, are women who have chosen this path and usually live in convents or monasteries. They engage in various forms of ministry and community service, often emphasizing prayer and contemplation as integral parts of their vocation.

Although the other terms—Brother, Priest, and Deacon—are also associated with roles within the Church, they serve different functions. A Brother is a male member of a religious order, while a Priest is someone ordained to lead worship and administer sacraments. A Deacon is specifically a minister who assists priests but is not part of a religious order in the same way that nuns or brothers are. Therefore, "Sister" or "Nun" specifically encapsulates the role of female members of religious orders within the context of the question.