What does stiff upper lippe reference mean?

[ItsJustMyShadow]

It could be reference to AC/DC but it's australian band and the achievement wants you to own Britain. Any ideas what does it mean?

[Fantastic Fwoosh]

The notion that British people have tightly held emotions and that its not socially accepted to be hysterical or show those emotions or upset in public (which to some degrees is true), we often express it as ``Keep Calm and Carry On``

• Lippe just completes the sentence for wordplay, nothing particularly symbolic about it.

[JVC]

Very nice description from Fantastic Fwoosh. The "real" expression is "to keep a stiff upper lip".