the "junior member", "member", and "senior member" are based on post count. I'm not really sure what the threshold is, but it's a few hundred at least. They're basically post ranks, and have no meaning other than indicating how many posts someone has made.
"banned" means the user has broken the rules, and is no longer allowed to post on the forum. In some cases, it may even mean the user can't view the forums (though I'm not sure what the policies are here).
"Career Officer" is a group that Lifetime members can join. It doesn't do anything but add a "status symbol"