An API (Application Programming Interface) is a defined set of rules and protocols that lets different software applications communicate with each other, exposing specific functionality without requiring one program to know how the other is built internally. A developer working with an API only needs to know what requests it accepts and what data it returns, not the underlying implementation behind it.
OpenAI, for example, offers an API that gives developers programmatic access to models like GPT-4, letting them send a prompt and receive a generated response directly within their own application, rather than through OpenAI's own ChatGPT interface. This is the mechanism that lets countless third-party products, from coding assistants to customer support tools, build on top of a foundation model without needing to train or host one themselves.
