sacred cowˌsacred ˈcow noun [countable] 
a belief, custom, system etc that is so important to some people that they will not let anyone criticize it: 
In New York’s show business scene, money, fame and power are sacred cows.
a belief, custom, system etc that is so important to some people that they will not let anyone criticize it: In New York’s show business scene, money, fame and power are sacred cows.