What does git push -u mean?

I have two different versions of git. In the 1.6.2 version, git push does not have the -u option. It only appears in the 1.7.x version. From the docs, the -u is related to the variable branch.<name>.merge in git config. This variable is described below: Defines, together with branch.<name>.remote, the upstream branch for the given branch. It tells git fetch/git pull which branch to merge. What is