Node.js is a revolutionary open - source, cross - platform JavaScript runtime environment. It allows developers to execute JavaScript code outside of a web browser, primarily on the server - side. Built on Chrome's V8 JavaScript engine, Node.js uses an event - driven, non - blocking I/O model, which makes it lightweight and efficient. This makes it well - suited for building real - time applications such as chat apps, streaming services, and web servers. The npm (Node Package Manager) associated with Node.js offers a vast repository of packages, enabling developers to reuse code and accelerate development. On the other hand, the Node Version Manager (NVM) is a handy tool for managing multiple Node.js versions on a single system. Different projects may require different Node.js versions due to compatibility issues. NVM allows developers to install, switch, and manage these versions with ease. For example, if a new project demands the latest Node.js features while an old one depends on an older version, NVM enables seamless toggling between them, ensuring smooth development across different projects.