Web Service is a software service used to communicate between two devices on a network.
More specifically, a Web service is a software application with a standardized way of providing interoperability between disparate applications. It does so over Hypertext Transfer Protocol (HTTP) using technologies such as eXtensible Markup Language (XML), Simple Object Access Protocol (SOAP), Web Services Description Language (WSDL), and Universal Description Discovery and Integration (UDDI).
Source: https://www.techopedia.com/definition/25301/web-service