What is an API?
API stands for Application Programming Interface, a concept that applies everywhere from command-line tools to enterprise Java code to Ruby on Rails web apps, and is defined as a specification of possible interactions with a software component.
An API is a way to programmatically interact with a separate software component or resource, and hide complexity from developers, extend systems to partners, organize code, and make components reusable.
Unless you write every single line of code from scratch, you’re going to be interacting with external software components, each with its own API. Even if you do write something entirely from scratch, a well-designed software application will have internal APIs to help organize code and make components more reusable.