A party or gathering held to welcome someone (e.g., a new employee or teacher).
入社初日の夜、部署のみんなが集まって歓迎会を開いてくれた。
On my first day at the company, everyone in the department got together and held a welcome party for me.
来週、外国から来る研究者のために歓迎会をする予定だ。
Next week we plan to have a welcome party for a researcher coming from abroad.
歓迎会では新しいメンバーが自己紹介をするのが普通だ。
At a welcome party it's common for the new member to introduce themselves.