Webservices are frequently just Web APIs that can be accessed over a network, such as the Internet, and executed on a remote system hosting the requested services.
The W3C Web service definition encompasses many different systems, but in common usage the term refers to clients and servers that communicate XML messages that follow the SOAP-standard.
Common in both the field and the terminology is the assumption that there is also a machine readable description of the operations supported by the server, a description in the WSDL.
The latter is not a requirement of SOAP endpoint, but it is a prerequisite for automated client-side code generation in the mainstream Java and .NET SOAP frameworks. Some industry organizations, such as the WS-I, mandate both SOAP and WSDL in their definition of a Web service.