What does it mean to be un-American?

After reading the Wikipedia article on the subject, which doesn’t really give a definition of what un-American should mean, I figured I might try to think about it myself.  What defines being American?  Since it only really concerns the government at the present time, it should be fairly easy to define. American We are free from enslavement by the government, and each other (well, unless we screw up, in which case the government can enslave us in prison).  We embrace [...]