Web services are not web applications. They are about the way we do with web applications. Foundation for Web Services includes:

• UDDI: publish, find, use services,
• WSDL: formal service descriptions,
• SOAP: service interactions,
• XML: universal data format, and
• the internet: ubiquitous communications.

The following are some good introductory reading about Web Services.

• The Essence of Web Services, written by Guillaume Pierre and Swaminathan Sivasubramanian,vrije Universiteit, in April 2004.
• Web Services Introduction from perfectXML.com. It is a very short one and contains good pointers.
• Top Ten FAQs for Web Services from oreillynet.com. It is good resource locator.