Definition
A place of great danger.
The phase of a startup business beginning with the entrepreneur's fulltime commitment to it and ending when the business has achieved sustainable cash flow.
Origins
Likely derived from the Old Testament, Psalm 23: valley of the shadow of death.
How People Actually Use It
The Valley of the Shadow of Death is a place where soldiers fight to the death and are protected by god above. God Save The Marines Semper Fidelis
"Today, we enter the Valley of the shadow of death. Men will die. Dead or Alive, We will leave no-one behind. I will be the first to step on the field and the last to step off."
Source: Urban Dictionary