Those two words make up an expression in my language, meaning something similar to "Nerves of Steel". Basically, this is used to describe someone who can stay calm even during the most trying situations. It can also be used as an exclamation, when things get tough, meaning one would love to have "Golden Nerves" in that moment.
However, it can also apply as a description of someone who knows how to relax.
Like Batcat. The way he can shut out the world is amazing. And highly contagious. The below is taken this weekend as he managed to escape into the dreamworld for hours, while lying in front of the fire.