What Does John Rawls Mean by the "Veil of Ignorance

What does John Rawls mean by the "veil of ignorance"?

A) When coming up with principles of justice, we should try to ignore our background.
B) People often refuse to analyze moral issues by using ignorance as a type of resistance.
C) We can never discover moral truths because they are hidden from us by a veil of ignorance.
D) It is ignorant of us to criticize women in other cultures for wearing veils since the principle of multiculturalism requires us to respect other cultures' customs.