What is API (Application Programming Interface)?
An API (Application Programming Interface) is a set of rules and definitions that lets one piece of software talk to another. It exposes specific capabilities or data through a stable contract, so developers can build on a system without knowing its internal details — much like a restaurant menu lets you order without seeing the kitchen.
Modern web products lean heavily on APIs: the front end calls back-end APIs, products integrate via third-party APIs (payments, maps, messaging), and platforms expose public APIs so others can build on top of them. REST and GraphQL are common styles.
PMs don't need to write APIs, but understanding them is essential. APIs can be a product in their own right (with their own roadmap, pricing, and developer experience), and they shape what integrations and partnerships are possible. "API as a product" thinking is core to platform and developer-facing PM roles.
Examples
- A product integrates Stripe's payments API instead of building a payment system from scratch.
- A PM defines rate limits, versioning, and docs as part of launching a public API.
Where PMs use this
Related terms
SDK (Software Development Kit)
A bundle of tools, libraries, and docs that helps developers build on or integrate with a platform.
Technical Debt
The future cost incurred when teams choose a quick or expedient solution over a better, slower one.
Feature Flag
A switch that turns functionality on or off in production without deploying new code.