This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
A web service is a service accessible using standard protocols over the web. The only strict requirement is that the messages being passed between the web service and the client are SOAP envelopes. The other two parts of the "classical" web services architecture are UDDI and WSDL. WSDL documents are used to describe the interface of a web service so that a developer (or a tool!) knows how to use that service. UDDI is an API for accessing a registry where service providers have published their web services for clients to discover (the UDDI API itself is actually based on SOAP messages).