API

The Application Programming Interface (API) is the digital contract that allows two separate software systems to communicate and exchange data, typically JSON, securely over a network.

An API is the essential communication layer: it defines the methods (GET, POST, DELETE) and the data structures (often JSON) for two distinct software applications to interact. This interface acts as a secure intermediary, managing authentication (via API keys or OAuth 2.0) and ensuring only authorized data is exchanged between the client and server. For example, the Stripe API handles billions of dollars in payments by exposing a single endpoint for a charge request, while the Google Maps API allows a third-party application to request and display complex map data, saving millions of development hours and enabling rapid feature deployment across the modern web.

https://www.postman.com/what-is-an-api/