What is an API?

An API stands for Application Programming Interface. At its simplest, it is a messenger that allows two different pieces of software to talk to each other.

Think of it like a restaurant:

• You (the user/application) are at a table, wanting to order food.
• The Kitchen (the server) is where the meal is prepared.
• The Waiter (the API) is the bridge. You give the waiter your order, they take it to the kitchen, and they bring the food back to you. You don’t need to know how the kitchen works; you just need the API to deliver your request and bring back the result.

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What is a REST API?

REST stands for Representational State Transfer. It is a specific set of "rules" or architectural constraints for building APIs.

If an API is the messenger, a REST API is a messenger that follows a very specific protocol to be efficient and predictable. It typically uses standard web protocols—specifically HTTP (the same language your web browser uses).

When you use a REST API, you interact with data using standard HTTP methods:

• GET: To retrieve information (like fetching a profile).
• POST: To create something new (like creating a new account).
• PUT: To update existing information.
• DELETE: To remove information.

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What is the difference?

The difference is a matter of category vs. implementation:

• API is the concept: It is the broad term for any interface that allows software components to interact. An API can be built in many different ways (e.g., SOAP, GraphQL, or old-school library files).
• REST is a style: It is one specific way to build an API.

Think of it like this:

• API is "Transportation."
• REST API is a "Car."

All cars are forms of transportation (all REST APIs are APIs), but not all forms of transportation are cars (not all APIs are REST APIs). Some APIs might be "trains" (SOAP) or "bicycles" (GraphQL), designed for different types of travel, but they all serve the core purpose of getting information from one place to another.