API (Application Programming Interface)
Pronunciation: AY-pee-eye
Also written as: API — Application Programming Interface
A defined set of rules and protocols that allows software components to communicate with one another.
Full Definition
An API specifies how software modules should interact, enabling developers to access functionality or data from an external service, library, or operating system without knowing its internal implementation. In developer-tools documentation, 'API' is always written as an acronym and should not be expanded on second reference. Editors should distinguish between REST APIs, GraphQL APIs, and library APIs, as these are not interchangeable terms. The plural is 'APIs', not 'API's'. When used as a modifier, it is typically left unhyphenated: 'API endpoint', 'API key'.
Usage
Usage note: Expand on first use only in non-technical audiences; treat as a known term in developer-facing docs. Never write 'API interface'—it is redundant.
In Context
- "The payment gateway exposes a REST API that developers can query to retrieve transaction histories." — Product documentation
- "Ensure all API references in the changelog link to the versioned reference docs, not the latest." — Editorial style note