WordPress is moving towards becoming a fully-fledged application framework, and we need we APIs. This project was born to create an easy-to-understand and well-tested framework for creating these APIs, plus creating APIs for the core.
Before we discuss the WP REST API, it’s important to understand some terminology and background information. The acronym API stands for Application Programming Interface. An API is a programmatic way to interact with an application’s data. For example, Facebook’s API gives developers the ability to get all of the friends associated with a certain user. An API typically includes a specific set of instructions called documentation; to make it easy for any developer to work with it.
REST means Representational State Transfer. An API can be considered RESTful if its design/architecture subscribes to a specific set of constraints.