In architecture, an atrium (plural: atria or atriums) is a large open-air or skylight-covered space surrounded by a building. Atria were a common feature in Ancient Roman dwellings, providing light and ventilation to the interior.

What is the plural form of the term atrium?

atri·​um | \ ˈā-trē-əm \ plural atria\ ˈā-​trē-​ə \ also atriums.

Is it called atria or atrium?

The upper two heart chambers are called atria. Atria are separated by an interatrial septum into the left atrium and the right atrium. The lower two chambers of the heart are called ventricles. Atria receive blood returning to the heart from the body and ventricles pump blood from the heart to the body.