title: What actually is an undefined?
body: <p>I am asking this question after reading <a href="https://stackoverflow.com/questions/5076944/what-is-the-difference-between-null-and-undefined-in-javascript">this</a> question.</p>
  
  <p><strong>NOTE</strong> I know the difference between <code>null</code> and <code>undefined</code>. </p>
  
  <p>Let me show you an example,</p>
  
  <pre class="lang-js prettyprint-override"><code>let a = {};
  
  console.log(a.test); // undefined
  </code></pre>
  
  <p>Now what if I add a property with <code>test1: undefined</code></p>
  
  <pre><code>a.test1 = undefined;
  
  console.log(test1); // undefined
  console.log(a); // { test1: undefined }
  </code></pre>
  
  <p>Now tell me what is <code>undefined</code>. Is it a value or something </p>