A listserv is rather like a mailing service. Everything you say, everyone else hears. And everything everyone else says you hear. This is done through email. Everyone who emails to the listserv has their email forwarded to everyone else in the listserv.
This situation is quite helpful if you are a member of a working group or special interest group that needs to share information or agree on things.
If you work with a specialized group, you may hear about appropriate and useful listservs by word of mouth. On the web, the best place I know of to look up listservs is the L-Soft site:
To learn all about listservs, read the manual at this location: