What does API stand for in tech? The answer is Application Programming Interface, a set of rules that lets one piece of software ask another for data or for an action, and get a predictable answer back. It is how programs talk to each other without needing to know how the other side works inside.
You use APIs all day without seeing them. When a weather widget on your phone shows the forecast, it is calling a weather service's API. When a shopping site shows a delivery map, or lets you pay with a saved card, APIs are passing requests and replies behind the scenes.
Quick facts
API full form
Application Programming InterfaceType
Initialism, said A P IPlural
APIsUsed in
Software, websites, apps, data servicesRelated terms
Endpoint, API key, REST, JSON, SDKOther meanings
Active Pharmaceutical Ingredient, American Petroleum Institute
What does API stand for, word by word?
- Application: any program or service, from a phone app to a bank's computer system.
- Programming: the requests are made by code, not by a person clicking buttons.
- Interface: the meeting point with clear rules, the way a wall outlet is the interface between your lamp and the power grid.
That outlet comparison is a good way to picture it. You do not need to know how the power plant works. You just need a plug that fits the shape the outlet expects. An API defines the shape: what you can ask for, how to ask, and what will come back.
A simple way to picture an API
Think of a restaurant. You do not walk into the kitchen. You read the menu, tell the server your order, and the server brings back food. In this picture:
| Restaurant | Software |
|---|---|
| Menu | The API documentation: the list of allowed requests |
| Your order | A request, such as "current weather for Denver" |
| Server | The API that carries the request and the reply |
| Kitchen | The other system, which does the work out of sight |
| Your plate | The response, often data in JSON format |
If you order something not on the menu, the server says no. Likewise, an API returns an error if a request does not follow its rules.
Where you meet APIs
- Maps on websites: a store locator shows a map by calling a mapping service's API.
- Signing in with another account: the "continue with" buttons rely on APIs that confirm who you are without sharing your password.
- Payments: checkout pages send card details to a payment processor's API and get back approved or declined.
- Travel sites: fare search pages gather flight data from many airlines' APIs at once.
- Smart home devices: an app turns on a light by sending a command to the device maker's API.
In a work email: "The order form is down because the shipping API is returning errors." Translation: the company's site asks a shipping service for rates, and that service is not answering correctly right now.
Terms you will hear next to API
- Endpoint: a specific address where one kind of request goes, usually a URL.
- API key: a long code that identifies who is making requests, like a membership card. Keep it private.
- REST: a common style of web API built on ordinary HTTP requests.
- SDK: software development kit, a bundle of tools and code that makes a particular API easier to use.
- Rate limit: a cap on how many requests you can send in a set time.
An API is not the same as a UI, or user interface. A UI is built for people, with buttons and screens. An API is built for programs, with requests and data.
Other things API can stand for
Outside software, the API acronym meaning changes with the field. Context usually makes it clear.
| Field | Stands for | Example |
|---|---|---|
| Technology | Application Programming Interface | "Our app pulls scores from a sports API." |
| Medicine and pharmacy | Active Pharmaceutical Ingredient | The part of a pill that does the medical work |
| Oil and gas | American Petroleum Institute | Motor oil labels and "API gravity" ratings |
| Demographics | Asian and Pacific Islander | A category on some surveys and reports |
Saying and writing API
Say each letter: "A P I." Write it in capitals without periods. The letter A is said "ay," so the article is "an": "an API," not "a API." Plural: APIs. Skip the apostrophe, which would signal possession.
A few example sentences:
- "The bank offers an API for business customers."
- "We hit the rate limit on the map API."
- "Read the API docs before you write any code."
- "Two of our APIs need new keys this month."
For more letters from software and the web, see the tech acronyms guide.
Questions people ask
What is API in simple terms?
An API is a messenger between two programs. One program sends a request in an agreed format, and the other sends back data or a result, so they can work together without sharing their inner workings.
Is the API abbreviation an acronym, and what is API short for?
Strictly speaking it is an initialism, since nobody tries to pronounce it like a word. Calling it an acronym in casual conversation is common, and nobody will be confused. API is short for Application Programming Interface.
Do regular people use APIs?
Yes, though not directly. Every time an app shows a map, checks the weather or takes a card payment, it is probably using an API behind the screen.
What is an API key?
It is a secret code that tells a service who is making a request. Services use it to track usage and block strangers, so it should never be shared publicly.
What does API mean on motor oil?
There it stands for American Petroleum Institute, a trade group whose service ratings appear on oil bottles. It has nothing to do with software.