formal tea gathering; formal tea party
A large, formal tea ceremony event, often with many guests and a structured program. Used in the context of Japanese tea culture.
I heard that a formal tea gathering will be held next month.
At a formal tea party, many guests enjoy tea at once.
A general term for a tea gathering, which can be small or informal. 大寄せ茶会 specifically refers to a large, formal event.
Compound of 大寄せ (large gathering) and 茶会 (tea party). The exact historical derivation is uncertain, but the term is used in tea ceremony contexts.