NodeJS is a server-side environment based on JavaScript. It was created in 2009 by Ryan Dahl, who wanted to improve the file upload progress bar on Flickr.
In a few years, Node became a reference for JavaScript developers and the community kept growing. Node is open source and gets several releases each year.
Strictly speaking, NodeJS is not a server environment per se. It is mostly about running and processing JS projects/applications on the server side rather than the client side (the browser). The principle is the same as PHP or a Ruby site: the code runs server-side.
Then you use plain HTTP to reach your JavaScript application.
Source: zdnet
