title: What does `setenv DISPLAY name:1001.0` mean in Linux?
body: <p>I'm doing some work using Linux server, after I log on to the server,the tutorial says:</p>
  
  <blockquote>
    <p>If you need to run any program which will open a window, like xterm, from these servers, you need to set display first.    </p>
  </blockquote>
  
  <p>To do that, I need to execute <code>setenv DISPLAY name:portnum</code>.What does this command really do?If I don't execute this command,what will happen?And what is xterm?</p>