Mailing list members are persons that have signed up for a given mailing list to receive regular email messages, such as weekly newsletters. If the mailing list client app that is used to administer the mailing list permits it, you can also approve mailing list members manually, but in this case such messages may be thought of as being unsolicited and reported as spam by the users. Basically, these members can unsubscribe from a mailing list by clicking a hyperlink in the emails they receive, or you, being the mailing list moderator, can delete them manually in case they request this or in case you decide that some of the mailing list members should not be part of the list any longer. Each member will see only their address in the "To" field of the emails they receive, but not the addresses of the rest of the members of the mailing list.