What's a Webring?

I just realized that I do not know what a webring is.... haven't heard the term in a long time, and not since I became so online oriented. I gather it's some kind of online community, but for some reason I associate it with listservs and such... Tonight I came across an "Edublog Webring" - now there's a combination! Anyways, that got me thinking..... Any insights will be most welcome...