Been a while since I've been here...
When an item is stickied it stays at the top of a dicussion/forum in this case this thread is under E30 discussions. An example of a sticky would the the administrators forum rules or attention messages such as the forums will be down.... If it was stickied it would be at the atop of all threads posted under E30 discussions no matter how old this thread is or new the newer threads are (normally new/updated threads appear at the top most of the discussion).
When were doing bump we were simply saying bump this thread above all other threads, thereby making it the topmost or one of the topmost threads in the E30 discussions. Thus bringing more attention to the thread.
Mad E30 lover