These are sites on the Internet that automatically maintain lists of individuals that share common interests. It costs nothing to subscribe to a mailing list.
Most lists are open and allow anyone to join.
Others are closed and are managed by someone who has to approve your name being added. Another method of communicating on the Internet is called Newsgroups. Newsgroups are different from mailing lists since rather than circulating each message sent to a group of subscribers, the messages are simply posted on the Newsgroup - like posting messages on a bulletin board. Users are able to review the list of newsgroups maintained by their ISP and see if they wish to choose and connect to any of them. There are thousands of newgroups and they are organized by type.