API

A defined interface that allows software systems to exchange data and actions.

01 · What is it?

What is it?

API stands for Application Programming Interface.

An API defines how one software system can request data or actions from another.

Simple Definition：
An API is a defined way for software systems to communicate.

02 · Think of it like...

Think of it like...

Think of an API as a service menu.

The menu tells you:

Software version：

Client→API→Service

03 · What does it do?

What does it do?

An API can allow software to:

Get Data

Create Data

Update Data

Delete Data

Trigger Actions

Connect Systems

04 · Where is it used?

Where is it used?

APIs are used between:

Frontend and Backend

Mobile App and Server

Internal Services

Business Systems

External Platforms

Cloud Services

05 · Example

Example

GET /api/orders

Purpose：
Retrieve orders.

POST /api/orders

Purpose：
Create a new order.

The method describes the action.
The endpoint identifies the API resource.

06 · How it connects

How it connects

Client→HTTP Request→API Endpoint→Backend→HTTP Response→Client

The API defines the available interface.
HTTP commonly carries the request and response.

07 · Do Not Confuse

Do Not Confuse

API

A collection of defined functions or resources available to other software.

Endpoint

One specific access point inside an API.

API = The interface
Endpoint = One address inside the interface

08 · Topic Glossary

Topic Glossary

ENGLISH TERM	中文	SIMPLE ENGLISH	中文小白理解
API	应用程序接口	A defined way for software systems to communicate.	让不同软件系统按照约定交换数据和调用功能的接口。
Endpoint	接口地址	A specific address that provides one API function.	API 中提供某个具体功能的访问地址。
Method	HTTP 方法	The action an API request wants to perform.	API 请求想执行的操作类型。
Request	请求	Data or instructions sent to an API.	客户端发送给 API 的数据或操作请求。
Response	响应	Data or a result returned by an API.	API 处理请求后返回的数据或结果。
Resource	资源	Data or an object exposed through an API.	API 对外提供访问的数据或业务对象。
Client	客户端	Software that calls an API.	发起 API 调用的软件一端。
Backend	后端	Software that commonly processes API requests.	通常负责处理 API 请求的软件部分。
HTTP	HTTP 协议	A common protocol used to call web APIs.	Web API 常用的基础通信协议。
JSON	JSON 数据格式	A common format used for API data.	API 请求和响应中常用的结构化数据格式。
API Documentation	API 文档	Documentation describing how to use an API.	说明接口如何调用、传什么、返回什么的文档。

09 · What to Remember

What to Remember

An API defines how software systems communicate.

An API usually contains multiple endpoints.

Web APIs commonly use HTTP requests and responses.

Final：
Client → API → Service