I'm reading a book about programming ASP.NET in C#. The book makes the following comment:

Previous editions of this book tackled web services, a feature that allows you to create code routines that can be called by other applications over the Internet.Web services are more interesting when considering rich client development (because they allow you to give web features to ordinary desktop applications),and they’re in the process of being replaced by a new technology known as WCF (Windows Communication Foundation). For those reasons, web services aren’t covered in this book.However,if you want to branch out and explore the web service world,you can download the web service chapters from the previous edition of this book from the book’s download page.The information in these chapters still applies to ASP.NET 3.5,because the web service feature hasn’t changed.

Can someone offer, in "layman's terms" what exactly a web service is and if, indeed, they are being replaced, at least in .Net, with WCF? What would be a practical example of a web service? Are they stand alone programs that run on a web server and are invoked by a client or clients?