I always check out Wikipedia for technology I not familiar with. Wikipedia has a good definition of a web service here ->
en.wikipedia.org/wiki/Web_serviceHere's my attempt at a definition (there's a lot more to web services then this - services lookup, QoS, security, transational support, etc.).
A web service is an open standards framework used to send messages between applications (and languages) over TCP/IP (Internet or intranet). You can use WSDL (WebServices Definition Language) to define the consumbable endpoint, the "method" invocation and the data that is use as part of the "method" signature and the expected response (and data type).
WAS supports a variet of current web services specs (see this link for more detail) ->
bit.ly/11McsBTI hope this helps.