One of the major impacts of the new communications technologies has been to increase the speed and ease of passing information between people. One manifestation of this is the development of newsgroups and discussion lists. The former are a means of disseminating information among a group of list subscribers, the latter a form of ongoing, online seminar to which interested parties can contribute.
You are usually required to sign on to these various lists in a prescribed manner. To get some idea of what they do have a look at the archive of the following lists: