Archives - The collection of all old messages.

Group - Often also known as a forum, a group is a place where people can post one message that is available to all other members of the same group.

Member – someone who is can participate in the group but not control it.
Moderator - someone who authorizes posts and/or members.

Owner - someone who runs a group.  This starts with the person who created the group, however later other people can be added to the list of owners.