Architecture
An API is a defined set of rules and protocols that allows one software application to request and exchange data or functionality with another, acting as a structured contract between systems.
APIs decouple the internal implementation of a service from the way external consumers interact with it, so a backend team can change database schemas or business logic without breaking third-party integrations as long as the API contract remains stable. Web APIs — the most common type today — communicate over HTTP and return data in formats like JSON or XML, making them language-agnostic and easy to consume from any platform. Public APIs allow companies to extend their product's reach (Stripe's payment API powers millions of third-party checkout flows), while private APIs connect internal microservices and system modules. Good API design includes versioning, authentication, rate limiting, and comprehensive documentation to support long-term maintainability.
Example
A food delivery app uses the Google Maps API to display real-time driver location on a map without building its own mapping infrastructure.
Related terms
REST API (Representational State Transfer API)
A REST API is a web API that follows the REST architectural style, using standard HTTP methods (GET, POST, PUT, DELETE) and stateless communication to expose resources identified by URLs.
GraphQL
GraphQL is a query language and runtime for APIs that allows clients to request exactly the data fields they need in a single request, eliminating over-fetching and under-fetching problems common in REST APIs.
Webhook
A webhook is an HTTP callback mechanism in which one application automatically sends a real-time data payload to a designated URL in another application whenever a specific event occurs, enabling event-driven integrations without polling.
Microservices
Microservices is an architectural style in which a large application is built as a collection of small, independently deployable services, each responsible for a specific business capability and communicating via APIs.
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