Node.js is an open-source, cross-platform JavaScript runtime environment built on Chromes V8 JavaScript engine. It allows developers to run JavaScript on the server side, enabling backend development with JavaScript.

NPM (Node Package Manager) is the default package manager for Node.js. It allows you to install, update, and manage packages or libraries for use in your Node.js projects. You can install packages globally or locally within a project.

Modules in Node.js are reusable pieces of code that can be included in other files. Node.js includes several built-in modules, such as fs (File System), http, path, and url. You can create custom modules or install third-party modules using NPM.