API vs Web Service

The terms API and web service are often used interchangeably, but there is a meaningful difference. An API (Application Programming Interface) is any interface that lets two pieces of software communicate.

A web service is a specific kind of API that is exposed over a network and uses web protocols such as HTTP. In other words, every web service is an API, but not every API is a web service.

Web services traditionally include SOAP and REST styles. REST, which uses standard HTTP verbs and typically exchanges JSON, has become the dominant approach for modern web and mobile applications.

The practical takeaway: when you need software components to talk to each other, you are using an API. When that communication happens over the web using HTTP, you are using a web service.