No essay on the nature of Usenet can ignore the erroneous impressions held by many Usenet users. Therefore, this section will treat falsehoods first. Keep reading for truth. (Beauty, alas, is not relevant to Usenet.)
What Usenet Is
Usenet is the set of machines that exchange articles tagged with one or more universally-recognized labels, called newsgroups (or "groups" for short). (Note that the term newsgroup is correct, while area, base, board, bboard, conference, round table, SIG, etc. are incorrect. If you want to be understood, be accurate.)
The Diversity of Usenet
If the above definition of Usenet sounds vague, that's because it is. It is almost impossible to generalize over all Usenet sites in any non-trivial way. Usenet encompasses government agencies, large universities, high schools, businesses of all sizes, home computers of all descriptions, etc.
Every administrator controls his own site. No one has any real control over any site but his own. The administrator gets his power from the owner of the system he administers. As long as the owner is happy with the job the administrator is doing, he can do whatever he pleases, up to and including cutting off Usenet entirely. C'est la vie.
What Usenet Is Not
Usenet is not an organization. Usenet has no central authority. In fact, it has no central anything. There is a vague notion of "upstream" and "downstream" related to the direction of high-volume news flow. It follows that, to the extent that "upstream" sites decide what traffic they will carry for their "downstream" neighbors, that "upstream" sites have some influence on their neighbors. But such influence is usually easy to circumvent, and heavy-handed manipulation typically results in a backlash of resentment.
Usenet is not a democracy. A democracy can be loosely defined as "government of the people, by the people, for the people." However, as explained above, Usenet is not an organization, and only an organization can be run as a democracy. Even a democracy must be organized, for if it lacks a means of enforcing the peoples' wishes, then it may as well not exist.
Some people wish that Usenet were a democracy. Many people pretend that it is. Both groups are sadly deluded.