one hall; one building; a single temple or shrine building
A formal or somewhat uncommon noun for one building or hall, especially a hall, temple, shrine building, or room-like structure. Modern everyday Japanese often uses more specific words such as 建物, 堂, or 部屋 instead.
山門の奥に小さな一堂が建っている。
A small hall stands beyond the temple gate.
same place; same room; same building
Usually used adverbially with に in formal phrases such as 一堂に会する and 一堂に集まる, meaning that people come together in one shared place.
全国の代表が東京に一堂に会した。
Representatives from across the country gathered together in Tokyo.
関係者が一堂に集まり、今後の方針を話し合った。
The people involved gathered in one place and discussed the future policy.
The graduates gathered together in one place.
They brought all the stakeholders together in one place to hold a meeting.