A joint party or mixer held by two or more groups (for example, student circles from different universities) to socialize and meet each other.
今週末は二つのサークルで合同コンパを開く予定だ。
This weekend the two clubs plan to hold a joint party.
合同コンパでは自己紹介タイムがあって、すぐに打ち解けやすい。
At joint mixers there's usually a time for introductions, which helps people warm up quickly.
男女混合の合同コンパは新しい出会いの場として人気がある。
Mixed-gender joint mixers are popular as places to meet new people.