LISTSERV is a mailing list program that was popular in the early days of the Internet. It was developed by Eric Thomas in 1985, but was not widely released until he made several revisions to make message distribution more efficient. The "Revised LISTSERV" program was released in June of 1986. It soon became the standard mailing list tool for BITNET, a network of United States universities.
Simplicity and automation were the main reasons LISTSERV grew in popularity. For example, it works over standard email, meaning you do not need special software to use the service. It allows you to subscribe and unsubscribe by simply sending an email to the correct email address. Once you subscribe to a LISTSERV list, you can send messages to all other members and receive messages from everyone who is subscribed to the list. Subscriptions and message distribution are handled automatically by the LISTSERV program.
LISTSERV provided an efficient medium for group discussions years before social media was available. But as email evolved, so did mailing lists. Over the years, more complex mass mailing systems have largely taken the place of LISTSERV. Even so, several universities still maintain LISTSERV servers, many of which have tens of thousands of subscribers.
NOTE: "LISTSERV" is sometimes used synonymously with "mailing list," but they are not the same thing. LISTSERV is a program that provides automated mailing list functionality. Many other mailing list programs and services besides LISTSERV are also available.