A Web Service is business logic accessed via standard Internet Protocols such as HTTP, SOAP, and WSDL. There is really nothing magical about them and the concept is plain ole RPC but it is just happening to catch on this time. Since a Web Service is accessible over standard protocols they can be used to integrate between disparate environments. In other words a Java Web Service can be accessed by a .Net Client and vica versa. I suggest getting a copy of Java Web Services by Dave Chappell(Sonic MQ) and Tyler Jewell(BEA). [ December 27, 2002: Message edited by: Chris Mathews ]
BTW, I noticed that you posted this same question in the Web Services/SOAP Forum. In the future please avoid from cross-posting. Many of us here read multiple forums and it is annoying to see duplicate posts.