A web service is an interface to interact with another application or with a database via an application programming interface (API).

Joomla 3.x has no built-in API that external software can use to retrieve information from a Joomla site. In a Joomla website a visitor requests web pages through a browser. These pages consist of HTML code to shape the page and data derived from an underlying database.

Via an API you can make available information from your Joomla website to other applications than web browsers.