API

Think of a restaurant. You don't walk into the kitchen and cook your own food. You look at a menu, tell the waiter what you want, and food appears. You don't need to know how the kitchen works. You just need to know what's on the menu.

An API is that menu. It's a set of rules that lets one piece of software ask another piece of software for something. Your weather app doesn't have its own weather satellites. It uses an API to ask a weather service, "Hey, what's the temperature in New York right now?" The weather service sends back the answer. Done.

Every time you log into a website with "Sign in with Google," that's an API. When Uber shows you a map, that's Google Maps' API. When you see a tweet embedded on a news site, that's Twitter's API. APIs are everywhere — they're the invisible plumbing that connects the entire internet.

Because APIs are how you can build powerful apps without building everything from scratch. Want your app to send emails? There's an API. Accept payments? API. Translate languages? API. Understanding APIs means understanding that you don't need to reinvent the wheel — you just need to know which wheels already exist.

An API (Application Programming Interface) defines a contract for how software components communicate. Most modern APIs are RESTful (using HTTP methods like GET, POST, PUT, DELETE) or use GraphQL. They typically exchange data in JSON format. Authentication is usually handled via API keys, OAuth tokens, or JWTs. Rate limiting and versioning are standard practices.