API
Application Programming Interface
A system that enables other programs to access and use a program's features and data
In Simple Terms
An API is like a "service window" where programs communicate with each other. It lets one app access and use the features or data from another app. For example, displaying Instagram photos on your own blog, or a weather app pulling data from the Japan Meteorological Agency — all of this is made possible by APIs. Because APIs exist, developers don't need to build everything from scratch — they can leverage existing features that others have already created.
Behind the Name
API stands for Application Programming Interface — each letter is taken from the first letter of each word. "Interface" means a point of contact or a service window. The name reflects exactly what it does: it acts as a "window" through which you access a program's features, and a "connecting point" where systems meet.
Take a Closer Look!
An API (Application Programming Interface) is a system that allows different software programs to exchange information and use each other's features.
When building an app or website, creating every feature from scratch would be an enormous amount of work. With APIs, you can incorporate useful features provided by other companies or services directly into your own app.
For example, when a restaurant review site displays a Google Map, or when a shopping site accepts credit card payments, each of those services is connected and working together through an API.
This means developers don't need to build maps or payment systems from the ground up — they can use existing, high-quality features instead.
In the case of a Web API, here's how it works: your program sends a request to the API — essentially saying "give me this data" or "please handle this process."
The system on the other side then processes the request and sends back the result as a response.