Node.js is an open-source server side runtime environment built on Chrome's V8 JavaScript engine. It provides an event driven, non-blocking (asynchronous) I/O and cross-platform runtime environment for building highly scalable server-side application using JavaScript.

Node.js can be used to build different types of applications such as command line application, web application, real-time chat application, REST API server etc. However, it is mainly used to build network programs like web servers, similar to PHP, Java, or ASP.NET.

Advantages of Node.js

• Node.js is an open-source framework under MIT license. (MIT license is a free software license originating at the Massachusetts Institute of Technology (MIT).)
• Uses JavaScript to build entire server side application.
• Lightweight framework that includes bare minimum modules. Other modules can be included as per the need of an application.
• Asynchronous by default. So it performs faster than other frameworks.
• Cross-platform framework that runs on Windows, MAC or Linux