Strictly speaking, a pledge brother is any person that is going through the same pledgeship as yours within a certain fraternity. And, they are in the same graduating class. They are the ones you bond the most with, and they are usually the ones that got your back for the rest of your life. Shit goes down when someone tries to mess with any of them. Their relationship is similar to that of a blood brother.
Joe: Honestly, if anyone happens to mess with my pledge brothers, they're fucked.
Mike: Yeah, same here. We're brothers in the bond.