Short answer
A REST API is the most common way to build an API for web systems. It uses ordinary HTTP requests — just like a browser — with clear addresses for resources (for example, /orders) and the actions GET (retrieve), POST (create), PUT/PATCH (change) and DELETE (remove). Data is usually exchanged in JSON format.
What a REST API looks like
GET /orders— get the list of orders.GET /orders/123— get a specific order.POST /orders— create a new order.PATCH /orders/123— change the order status.
The response comes in JSON — structured text that any programming language can easily process.
Why REST is so widespread
- Simple and easy to understand.
- Works over ordinary HTTP, just like websites.
- Supported by practically every programming language and framework.
- Easy to document — often with an OpenAPI (Swagger) description.
Other kinds of API
- GraphQL — the client specifies exactly which data it wants to receive.
- SOAP — an older, XML-based standard still used by many government and banking systems.
- Webhook — one system notifies another about an event by itself.
For API development we often use API Platform with Symfony, which generates documentation automatically from the code and supports REST and GraphQL.