noun
joint meeting
A meeting held jointly by two or more groups, organizations, or committees.
来週、両社の合同会合が予定されている。
A joint meeting of the two companies is scheduled for next week.
合同会合で新しい方針を決めた。
We decided on a new policy at the joint meeting.
合同 means 'joint' or 'combined' and is used as a prefix in compounds like 合同会合, 合同練習 (joint practice), etc.
Compound of 合同 (ごうどう, 'joint, combined') and 会合 (かいごう, 'meeting, gathering').