Definition: An API (Application Programming Interface) is a defined way for software components to communicate using requests and responses. It specifies available operations, input formats, output formats, and error handling, so different programs can work together reliably. APIs may be local, between processes on one machine, or remote over a network using protocols like HTTP. Public APIs expose services to external developers, while private or internal APIs support a company’s own systems. Styles include REST, GraphQL, and gRPC. Good APIs document endpoints, authentication, rate limits, and versioning, and often publish schemas such as OpenAPI for tooling and testing support. Monitoring tools track real usage.
Example: A weather app uses a forecast API to fetch tomorrow’s temperature in Celsius.
Also called: Application Programming Interface
Related: HTTP (Hypertext Transfer Protocol), REST (Representational State Transfer), GraphQL, OpenAPI Specification (OAS)