Mailing list members are persons that have registered for a particular mailing list to get periodic emails, including weekly newsletters. In case the mailing list client application that is used to administer the list permits it, you can also add members manually, but in this case such emails may be accepted as unsolicited and reported as spam by the recipients. Basically, these mailing list members can unsubscribe from a mailing list by clicking on a link in the email messages they receive, or you, being the mailing list admin, can manually remove them if they make such a request or if you decide that some of the mailing list members should not belong to the list anymore. Each mailing list member will see only their address in the "To" field of the messages they get, but not the email addresses of the rest of the mailing list members.