How does a Node.js "server" compare with Nginx or Apache servers?

I have been studying Node.js recently and came across some material on writing simple Node.js based servers. For example, the following. var express = require("express"), http = require("http"), app; // Create our Express-powered HTTP server // and have it listen on port 3000 app = express(); http.createServer(app).listen(3000); // set up our routes app.get("/hello", function (req, res) { res.send("Hello World!"); }); app.get("/goodbye", function (req, res) { res.send("Goodbye World!"); }); Now, although I seem to understand what's going on in the code, I am slightly confused by the terminology. When I hear the term server, I think about stuff like Apache or Nginx. I am used to thinking about them as being like a container that can hold my web applications. How does Node.js server differ from Nginx/Apache server? Isn't it true that a Node.js based server (i.e. code) can still be placed within something like Nginx to run? So why are both called "servers"?