A gathering or party held to send off someone who is leaving (e.g., retirement, transfer, graduation).
明日、部署で山田さんの送別会があります。
Tomorrow there's a send-off party for Yamada in our department.
送別会ではみんなで花束を渡して、写真を撮った。
At the farewell party we gave a bouquet to him and took pictures.
大学のゼミで小さな送別会を開いて、スピーチを頼まれた。
We held a small send-off party in the university seminar, and I was asked to give a speech.
今回は歓迎会と送別会を同じ日に行うことになった。
This time we decided to hold the welcome party and the send-off party on the same day.