People who share the same status or situation; often used as a suffix (〜同士) to mean 'among' or 'fellow' (e.g., 仲間同士).
部活動の仲間同士で旅行に行った。
I went on a trip with my clubmates.
学生同士で助け合うのは大切だ。
It's important for students to help one another.
友達同士の会話はリラックスした雰囲気だ。
Conversations among friends have a relaxed atmosphere.