The real meaning of a clan is a tribe, group, or mainly family. If you think all clans are barbaric, you will offend many people.

Anyway, JJ2 clans are mainly just so you can brag about it. Also, it's nice for meeting new people, I guess, but we mainly know each other already. Also, sometimes, clans have team wars on JJ2, like Team Battle or CTF, just for fun. Usually, clans have tests to get in, but some don't. There are a few considered "the best", but they're usually the most known. There's really no official way to rate a clan.