A listserv is an automated mailing list used to send email to a goup of people interested in a particular topic. When a message is sent to a listserv email address, the message is automatically distributed to everyone currently subscribed to the list. Most lists require you to subscribe to the list before you can send a message to that list.
There are two types of lists: unmoderated and moderated. An unmoderated list encourages a free flow of information because no one reviews it. When someone sends a message to the list, the message to is sent to all subscribers. With a moderated list, all messages are reviewed before they are sent to all subscribers. A designated moderator examines it to make sure it is appropriate.