Bartenders are people that have been recognized as generous, decent, helpful people and given the keys to a forum to do moderating as they see fit. They can edit, delete, or prune any posts in their forums. If you have a question about a particular forum, you should direct it to (one of) the forum's bartender(s).
Friendly, helpful people who participate frequently in the forums over a long period of time may be invited to become bartenders. It's an unwritten rule, by the way, that asking to be made a bartender is the quickest way to make sure you never get to be one