User blog:DirtLover03/What is the "USERNAME" Template?

So I was on the wiki recently, and I decided to edit my wiki page by adding some templates like what platforms I own Minecraft on. There was also a template called "USERNAME" and I was wondering what it was so I clicked learn more about this template and when I was sent to the page to learn more about it I saw this. Can someone please tell me what the purpose of the USERNAME template is and why has it redirected me to this page? And why is it calling me an idiot? So can someone please comment on this post and tell me what it is.