git push でエラーが出ます。

$ git push
Counting objects: 9, done.
Compressing objects: 100% (5/5), done.
Writing objects: 100% (6/6), 924 bytes, done.
Total 6 (delta 3), reused 0 (delta 0)
To [email protected]:myname/project.git
3648514..9fc4c3a ot -> ot
! [rejected] master -> master (non-fast forward)
error: failed to push some refs to '[email protected]:myname/project.git'

これはどういう意味で、どう対処すればいいでしょうか。