What is an Express.JS App?

The basis of my question is the "Hello World" example at:

http://expressjs.com/starter/hello-world.html

It's just 10 lines of code. One of the relevant statements is:

var app = express();


Which is followed by:

var server = app.listen(3000, function () {


The app.listen() method appears to be instantiating an HTTP services. Is
that to say that each express.js application includes its own HTTP service?

Personally, I tend to scope Web "applications" to handle perhaps 10-15
distinct types of requests. An application for querying and maintaining
Purchase Orders would be distinct from one which queries and maintains Work
Requests, for example. That keeps the code modular.

We have deployed 500+ "applications" of that type of scope.

Using Express.JS, would you deploy 500+ HTTP server instances?