title: NODE_ENV variable in Node.js
body: <p>I am a beginner in Node and I see the following code in my project:</p>
  
  <pre><code>process.env.NODE_ENV
  </code></pre>
  
  <p>What is <code>NODE_ENV</code> and how can I get access to it or change it? It seems to pick up some values but don't know from where is it getting picked up.</p>
  
  <p>Please let me know.</p>