A Disqus shortname is the URL prefix of your Disqus account. It links your Tumblr blog to your Disqus account so your readers can post new comments and reply to other readers' comments about your Tumblr blog posts. This helps you create conversations around the topics you write about and helps build a community around the key issues you discuss in your blog.
To add Disqus to your Tumblr blog, you must sign up on the Disqus website and enable Disqus on your blog using your Disqus URL prefix, or shortname.
Click the Facebook, Twitter or Google Plus icons to sign up with your credentials from that site. Or type your name, email and a password and choose Sign Up. You must confirm your email by clicking the link in an email message from Disqus if you choose the email signup option.
Log in to your new Disqus account. Click the Gear icon in the upper-right corner of the screen and choose Add Disqus to Site.
Type the name of your blog and either accept the default Disqus URL or type your own prefix for your disqus.com URL. This is the shortname you must include on Tumblr. Select a category and choose Finish Registration to continue.
Choose Tumblr for your platform.
Review the instructions to add Disqus to your blog.
Log in to Tumblr and choose Edit Appearance from the menu.
Select Edit Theme.
Type your Disqus shortname to integrate Disqus into your Tumblr blog and theme.