noun
main party; first party
Refers to the first, main gathering of an evening, often a dinner or formal event, before moving to a 二次会 (after-party). Common in social and business drinking contexts.
See also: 二次会
一次会はレストランで、二次会はカラオケに行く予定です。
The main party will be at a restaurant, and then we plan to go to karaoke for the after-party.
一次会だけ参加します。
I'll only attend the first party.
二次会 is the after-party or second gathering, often more casual, following the main 一次会.
Compound of 一次 (first, primary) and 会 (meeting, party).