A Google Group is a user-owned group created using the Google Groups service.
Google Groups not only allows you to manage and archive your mailing list, but also provides a method for true communication and collaboration with group members.
Unlike other free mailing list services, Google Groups offers generous storage limits, customizable pages, and unique management options.
As always, Google Groups displays only relevant text ads (never banners or pop-up ads).
(Info copied from Google Groups Help – 28th Jan 2008)