Interface
The agreed meeting point where two parts of a system exchange requests and answers.
Glossary
Application Programming Interface (API)
A defined set of requests one piece of software can make of another.
In one line
A defined set of requests one piece of software can make of another.
Also calledprogramming interface
An API is a published list of things you are allowed to ask for, and the form your request must take. It lets separate programs cooperate without being woven together. One program offers the list; another reads it and knows exactly how to ask.
When a program wants something from hardware, it makes a standard request through an API. A driver listens for those requests and turns them into the specific actions one component understands. The program never has to know the device's private details; it only has to know the published list.
A well-designed API is steady and clear. It changes slowly and keeps its old promises, because every program that relies on it would be disturbed by sudden change. This reliability is what lets software built by different people, at different times, fit together.
An API also draws a helpful line of responsibility. The side that offers it is free to improve everything behind the line, while the side that uses it can depend on the surface staying the same. That separation is part of what keeps large software systems from collapsing under their own complexity.
In practice
In practice, an API is like a restaurant menu. You read the listed dishes and order by name; you do not walk into the kitchen or explain how to cook. The kitchen can change its methods freely, yet your order still works, because the menu is the agreed, published way to ask.
