What is the difference between GitHub username and GitHub ID? I was asked for my Github ID for a certain project and I happened to give my username. But the person is unable to find me on GitHub with my username. So I got a GitHub ID from the below URL:

http://caius.github.io/github_id/

But I'm unable to find this ID from my account directly. Where can I find this in my GitHub account? It would be great to elaborate on this.