Web Service is a data or application that is accessible via the standard web protocol such as HTTP or HTTPs. Just like a web application, Web Services are also designed to communicate with other programs, rather than directly with the visitors.
The services provide data in the number of different formats, and the most common format includes XML and JSON. These standard formats can be easily recognized and parsed by another application that receives the data. Common web service protocol includes SOAP.
All the business-oriented web services may use the standard known as UDDI. This formats data in the specific type of XML called the Web Service Description Language or WSDL. While UDDI transmits .wsdl file instead of a .xml file, it may still use the SOAP protocol to transfer data.
Most of the web services provide an API, set of function and commands that can be used to access the web data. i.e., the most popular social media platform Twitter provides an API that enables the developer to access tweets from the service and receive the data in JSON format.