Note: Usenet is also known as "Newsgroups", net news or simply news.
Usenet is a distributed message system dating back to the early 1980s. It is still widely used, and a very good way to communicate with others anywhere in the world about any topic. It is similar to modern systems such as Yahoo Groups, but is more universal and standardized. Google sponsors a searchable database of all public Usenet groups.
Usenet users can easily create their own categories and choose to "host" others' categories for users in their community.
One of the many things one could find on Usenet was the UCDavis Usenet FAQ.
UC Davis has its own ucd.* heirarchy, which contains groups for general discussion, campus organizations, courses, and more. Aside from some Computer Science course newsgroups and ucd.swap, most of them are unused. Some of these are propagated to other news servers (except for ucd.class.*) and you may be able to access them from another ISP. To access all the ucd.* groups, you must use the news.ucdavis.edu NNTP server or web interface. You will need a UCD login to access them.
On a historic note, before internet access was generally available, usenet was accessible to Davis residents via local BBSes.