There are two primary administrative roles for each mailing list, a list owner and a list moderator. A list owner is allowed to change various settings of the list, such as the privacy and archiving policies, the content filtering settings, etc. The list owner is also allowed to subscribe or invite members, unsubscribe members, and change any member's subscription options.
The list moderator on the other hand, is only allowed to approve or reject postings and subscription requests. The list moderator can also do things like clear a member's moderation flag, or add an address to a list of approved non-member posters.
Normally, the list owner and list moderator are the same person. In fact, the list owner can always do all the tasks a list moderator can do. Access to both the owner's configuration pages, and the moderation pages are protected by the same password. However, if the list owner wants to delegate posting and subscription approval authority to other people, a separate list moderator password can be set, giving moderators access to the approval pages, but not the configuration pages. In this setup, list owners can still moderate the list, of course.
In the sections that follow, we'll often use the terms list owner and list administrator interchangably, meaning both roles. When necessary, we'll distinguish the list moderator explicitly.