I'm reading the following article: http://github.com/guides/keeping-a-git-fork-in-sync-with-the-forked-repo, where they mention essentially pulling in changes from two repos at the same time by creating the following alias:

pu = !"git fetch origin -v; git fetch wycats -v; git merge wycats/master"

This makes sense, but, as someone new to Git, I'm curious why the commands is that versus:

pu = !"git fetch origin -v; git merge origin/master; git fetch wycats -v; git merge wycats/master"

or something along those lines. Basically, I'm wondering why the argument to merge is wycats/master and how it knows about origin/master automatically. Looking for a quick explanation.