A newsgroup is another name for a usenet group. It's far older than the WWW, which made groups like Mudcat possible. Your access depends on your internet provider but search your provider's pages for news, newsgroups or usenet to see how you can get it.

Here's one page with information. There may be better ones around.
Usenet stands for "User's Network", is often called the "newsgroups", and consists of tens of thousands of virtual bulletin boards on different subjects available around the world. Anyone with access to the Internet can post a message to any newsgroup, read any message, and post a response to any message on the Usenet.

The Usenet is a useful place to turn when searching for the answer to a question since so many questions are asked and answered there, and when looking for information about late-breaking or underground subjects likely to be part of popular conversation.

Until recently you could interact with Usenet via DejaNews. That's gone but If you go to Google's pale imitation of Deja & click through the rec. then music. then celtic links, you'll find the conversation of a few days ago.