What does 'stiff upper lip' mean?

Answer 1

It is typical of the British. I suspect it is British/Indian in origin & is descriptive of a lack of emotion, or at least visible emotion. Apparrently it comes from the novellist PG Wodehouse in 1924, or at least it was popularised by him.

Answer 2

This idiom means to take on information/pain stoicly (i.e without reaction). This expression specifically means to carry on as you were and not let the world see how you are feeling.

e.g

Adam:"My nan just died"

Ben: "Ah well Stiff upper lip and all"

A similar idiom is "keep your chin up".
There are many meanings that one might accept as a stiff upper lip. The actual meaning of a stiff upper lip is when one has self restraint especially in situations where crying might ensue. In situations where crying might ensue a stiff upper lipped person would not cry.
It refers to the idea that your lips tremble when crying or upset and that 'keeping a stiff upper lip' would mean to suck it up and not cry.
To keep a stiff upper lip is to show courage and bravery, also self-restraint. It refers to involuntary spasms of the mouth preliminary to weeping. By keeping a stiff upper lip, we put on a brave face.