What is a web ring? Simple -- a web ring is a grouping of web sites on a particular topic. The sites in the ring link to one another in a loop that surfers can follow around.
The idea is this: once you've found one site on a topic that interests you, and if that site is part of a web ring, you can explore the ring to find other sites that will interest you. Web rings are great for web surfers: they allow you to easily find and explore many sites related to a subject.
When a site belongs to a web ring, it features a set of controls for navigating the ring. Common controls include "next" (for moving to the next site in the ring. Keep in mind that there's not a start or end to the ring -- press "next" enough and eventually you'll end up back where you started), "previous" (for moving backward) and "random" (for the true surfer, this will punt you to a random site in the ring). Most rings provide an index page, where you can see an overview of all the connected pages and jump to any one that looks especially interesting.
Ready to be overwhelmed? There are web rings about almost everything, covering just about any topic you can imagine. The Web's de facto center for web rings is http://www.webring.com. This free site is an index to tens of thousands of web rings. Search its directory: you'll find rings devoted to literature, medicine, philosophy, pets, civil rights, science fiction, and science fact. Each ring might encompass any number of pages, from two to hundreds.
If you've created a web site of your own, joining a web ring can be a great way to build traffic to your site and be found by people who are truly interested in its subject. You'll just have to find a relevant ring and request to have your site added. It doesn't matter if your page's subject matter is conventional or offbeat, chances are there's a ring that it will fit into nicely. Joining a ring won't cost anything but it's not an automatic process: the person who oversees the ring must approve your site -- if your site fits into a ring's theme, it should be approved without any fuss. Also, you'll need to add an "HTML fragment" somewhere on your web page (perhaps near the bottom of its home page) which includes the web ring's graphic and buttons. (When you request to join a ring, you'll be given the specific HTML fragment for that ring.)
If there isn't already a ring on the topic that your page covers, you can start your own. If you decide to create a new ring, you'll be the "ring master," the person who decides what other sites may be added and performs other administrative tasks. Of course, if you start your own ring, your site will be the only one in the ring -- that is neither interesting nor a way to increase the number of visitors to your site. So you should consider sending e-mail to invite the creators of other relevant sites to join your little web ring. (If you can't find any other sites that would fit in, maybe your proposed web ring is a little two narrowly defined, eh?)
Web rings are an increasingly popular phenomenon. They're useful for surfers and good for web site creators, too. The next time you happen upon a page that's part of a ring, go ahead and use it to explore.