An after-party or second party (e.g., after the main party or reception); a follow-up social gathering later the same night.
結婚式のあと、友人たちと二次会に行った。
After the wedding I went to the after-party with friends.
飲み会は一次会で終わりにするつもりだったが、結局二次会まで行った。
We intended to end the drinking party after the first round, but we ended up going to the second party.
二次会はカラオケを予約してあるから、遅れないでね。
We reserved karaoke for the after‑party, so don't be late.
A second meeting (e.g., a follow-up meeting or additional session after an initial meeting).
当初の打ち合わせで決まらなかったので、翌週に二次会を開くことにした。
Since we couldn't decide in the initial meeting, we decided to hold a second meeting the following week.
二次会では予算案の詳細を詰める予定だ。
In the second meeting we plan to finalize the budget details.