What are modules in Node.js?

Modules are reusable blocks of code in Node.js that help in organizing and separating functionalities. Node.js uses CommonJS module system where you can export and import functionalities between different files. For example:

// myModule.js
const greeting = 'Hello, World!';
module.exports = greeting;
// app.js
const greet = require('./myModule');
console.log(greet); // Outputs: Hello, World!