A weather app on your phone does not measure temperature itself. It asks a weather service for data. That conversation happens through an Application Programming Interface, or API — a set of rules allowing software programs to communicate. The API defines what requests can be made, what format they take, and what responses come back.

Think of it as a menu in a restaurant. You do not walk into the kitchen and cook. You order from a list of dishes. The API is the menu. The kitchen is the server. You get your food without knowing how it was prepared.

Common API styles

• REST: uses HTTP methods like GET and POST, widely used on the web
• GraphQL: lets clients request exactly the data they need
• SOAP: older, formal, still used in banking and enterprise
• Webhooks: server sends data when an event happens

APIs power much of what you do online. When you log in with Google, pay with PayPal, or share a post to social media, an API is doing the work. They are the connective tissue of the internet.