An API stands for “application programming interface” and is a way of using a service. APIs have their own set of rules that vary from service to service. Most APIs use the same data transport mechanism as the web, with GET and POST methods. Python has a built-in library called URLLIB, but it’s more convenient to use a specialized library called requests for making requests of APIs. JSON (JavaScript Object Notation) is a common data format for APIs that’s easy for both humans and computers to read and write. JSON data can flow in and out of Python easily, but it’s important to understand the concept of flattening data as it flows between systems. APIs have their own little APIs for accessing the data inside them, but these go away when the data is flattened into a string. The ability to pass data between different systems is called portable, interoperable data.

source: The Moz Links API: An Introduction