 <p><code>express</code> is a module that can be used to create more than one application.</p> <pre><code>var ex = require('express') </code></pre> <p>puts this module into the variable <code>ex</code>. Once you have a reference to the module, you can use it to create application. Each module has its own API. According to the expressjs documentation - <a href="http://expressjs.com/en/4x/api.html" rel="nofollow">http://expressjs.com/en/4x/api.html</a>, the module is in fact a function that can be used to create applications</p> <pre><code>var app1 = ex(); var app2 = ex(); </code></pre> <p>you could for example want to have several web applications listening on different ports.</p> <p>If you only want one application (but it would be less readable) you could write</p> <pre><code>var app = require('express')(); </code></pre>