API (Application Programming Interface) is a piece of software that enables data exchange between applications and devices., as well as facilitate connectivity between devices and programs.
API can also be defined as an interface that allows an enterprise application to communicate with backend systems, promotes seamless communication between multiple applications, and exposes only a limited amount of the internal functions of a program.

The following image is the visual representation of API functions and procedures .

APIs are a set of functions and procedures allowing the creation of applications that access the features or data of an operating system, application, or other service. 2gole API Integration Overview
API is a collection of defined functional endpoints for communication with a host tool.
Application Programming Interface (API)is a software intermediary that allows two applications to talk to each other.
Provides developer experience across all kinds of applications and services
Connects all different applications in a seamless manner
Creates an omni channel customer experience
Built on common set of REST APIseracts with: filling out a form, creating a profile, shopping online, etc.

How Crucial Is the REST API Design in an API Integration Scenario?

Primarily APIs are used to establish a link between applications and devices.
Crafting a proper REST API can help build functional integration between the required components. However, wrong implementation could compromise the entire project.
To implement a good Rest API design architecture, you need to follow some basic rules, which are as follows:
Know the applications and the associated use cases before the intended implementation.
It is very important to know the HTTP constraints.
Follow the architecture and the binding framework used for engineering.
Ensure proper handling of already exposed end-point changes.