What is the difference between origin and upstream in github

This should be understood in the context of GitHub forks (when you clone a GitHub repo at GitHub, before cloning that fork locally)

• upstream generally refers to the original repo that you have forked
  (see also "Definition of “downstream” and “upstream”" for more on upstream term)
• origin is your fork: your own repo on GitHub, clone of the original repo of GitHub

From the GitHub page:

When a repo is cloned, it has a default remote called origin that points to your fork on GitHub, not the original repo it was forked from.
To keep track of the original repo, you need to add another remote named upstream

git remote add upstream git://github.com/user/repo.git

You will use upstream to fetch from the original repo (in order to keep your local copy in sync with the project you wanted to contributed to).

You will use origin to pull and push since you can contribute to your own repo.

You will contribute back to the upstream repo by making a pull request.

http://stackoverflow.com/questions/9257533/what-is-the-difference-between-origin-and-upstream-in-github/9257901#9257901