A taboo is a vehement prohibition of an action based on the belief that such behavior is either too sacred or too accursed for ordinary individuals to undertake, under threat of supernatural punishment. Such prohibitions are present in virtually all societies. The word has been somewhat expanded in the social sciences to strong prohibitions relating to any area of human activity or custom that is sacred or forbidden based on moral judgment and religious beliefs. "Breaking a taboo" is usually considered objectionable by society in general, not merely a subset of a culture.
“Taboo means prohibited talks especially of religion.
eg: Things once were taboo are now discussed openly.”