Answer:
"The valley of the shadow of death" means the concentration camps or the place where the Jews were tortured and killed.
Step-by-step explanation:
Elie Wiesel first wrote his "Night" about his personal experiences during the famous holocaust. When the Germans army under their dictator Hitler began ostracizing and hunting for any Jews in the country, Elie Weisel and his family were part of the Jews captured due to this order. Jews were thought to be the sworn enemies of the land and they should be removed from the face of the earth. So, Hitler began hunting for any Jewish people.
The preface of the memoir contains the lines "the valley of the shadow of death" which is also based on the biblical verse from Psalm 23. This verse from the Bible talks of the speaker's faith in God and how he will have no worry wherever he goes. The verse goes like this-
"even though I walk through the valley of the shadow of death,
I will fear no evil, for you are with me
your rod and your staff, they protect me".
This phrase means any obstacle that may come in the life of a Christian, in whose trust is God. So, God will always rescue them and not leave them alone.
Likewise, in the preface written by Robert McAfee Brown, the phrase is mentioned. But here, the phrase means the literal place of the concentration camps that serve as the homes of the captured and imprisoned Jews. This was the valley which everyone feared to go through or even be nearby.