REST API vs Web API

What is the difference between API and REST API?

Not all APIs are REST, but all REST services are APIs

So let's start a common difference between API and REST API.

• API Stands for (Application Program Interface) and REST stands for (Representational State Transfer)
• The Function of API is to connect one application to another application. You can say that it is a connector between two applications. On the other hand, REST API build the connection between Client and server using URL and HTTP protocols. 
• REST API's are widely used for exchanging data between systems or applications. API provides product or service to communicate with other products and services without having to know how they're implemented.
• API is a set of functions and procedures that allow one application to access the feature of other application.
• API supports CRUD (Create Read Update Delete) actions as it works with HTTP verbs GET, PUT, POST, and DELETE. 
• REST API is a web service that supports only HTTP protocol whereas API supports HTTP/HTTPS protocol.
• Web service supports XML while API supports XML and JSON

REST API's Provide ability to support remote procedure calls and they are loosely coupled as well. The main reason to excessive use of REST API's because it requires limited resources, fewer security requirements and browser compatibility and scalability as well.