The Interactive Glossary: Defining the Net
A mailing list is a way of having a group discussion by electronic mail and distributing announcements to a large number of people. A mailing list is very much like participating in an online group, except that the conversation comes to you in your e-mail Inbox. Each time you or any member of the list posts a reply to the conversation, it is e-mailed to every member of the list. All of this traffic is automated and managed by programs called mailing list managers (MLMs). The two frequently used programs are Listserv and Majordomo.
Learn more: Mailing Lists