The name pretty much says it all. Lots of good stuff. Quite often you can get answers put in by Oracle staff, so obviously they watch, making it a good place to put open letters to Oracle, or discuss Linux. There is a fair bit of advocacy here, and stuff that should be in comp.databases.xbase or whatever, but if you are into interfacing or comparing software, then this is a good place to go. Mailing lists are programs that receive mail from subscribers, and then mail all the other subscribers to the list.
Some network nodes look after a number of lists.
Sometimes a list is run by a private moderator. Most lists have a moderator, who is a benevolent dictator, setting standards of behaviour, and with the absolute right to eject anybody who breaks the rules. If you are not a subscriber, then your mail will simply be bounced back at you. Oracle-L This is a general purpose list on Oracle. The volume varies, but it can get quite high.