An API, or Application Programming Interface, is a set of rules that lets one program request something from another and get a response back. Think of it as a waiter: you do not go into the kitchen yourself; you place an order through the waiter and the food comes back. Software uses APIs to order data or actions from other software.
APIs are how AI gets built into the apps you use. When a writing app offers an "AI" button, it is usually calling an AI model's API behind the scenes — sending your text to the model and showing you the response. Our own AI tools work this way. APIs are also how AI agents take actions in other systems.
Related terms
AI Agent · Large Language Model (LLM)