Taboo refers to matters that are forbidden; it expresses itself essentially in prohibitions and restrictions. In practice, taboo is the ritual avoidance of things, persons, places, times, actions or words believed to be inauspicious or, on the contrary, sacred.
Taboo was originally the negative aspect of magic, being something forbidden or profane; its modern equivalent is prejudice, which in popular usage can also include hypocrisy since subjects which are a source of embarrassment are often denied and 'taboo'. Taboos in primitive society constitute barriers to technological progress; in developed society, although they may also constitute barriers to technological progress, they are more significantly barriers to social progress.
Taboos are widespread among indigenous populations. The Ark of the Covenant and the Holy of Holies were taboo to the ancient Israelites. The caste system of India is an extraordinary complex of taboos. Incest is taboo for all societies. In Japan the number four 'shi' is avoided because it is a homonym of the word death 'shi'.
Being founded in religion, taboos are strictly observed by the societies to which they are relevant; a lack in observance of taboos by development planners may bring about project failure. In so far as advanced technology is very strange to indigenous tribes, it may itself be subject to taboos. Taboo in the sense of social prejudice is widespread in developed societies, particularly where they are strongly pluralistic; taboo in the sense of hypocrisy is also widespread, but both this and prejudice is alleviated to some extent by an increase in education and cultural integration or assimilation.
Every society has taboos and they are a rational and systematic derivatives of the basic postulates of the society.