A taboo, also spelled tabu, is a social group's ban, prohibition, or avoidance of something (usually an utterance or behavior) based on the group's sense that it is excessively repulsive, offensive, sacred, or allowed only for certain people. Such prohibitions are present in virtually all societies. Taboos may be prohibited explicitly, for example within a legal system or religion, or implicitly, for example by social norms or conventions followed by a particular culture or organization.
Taboos are often meant to protect the individual, but there are other reasons for their development. An ecological or medical background is apparent in many, including some that are seen as religious or spiritual in origin. Taboos can help use a resource more efficiently, but when applied to only a subsection of the community they can also serve to suppress said subsection of the community. A taboo acknowledged by a particular group or tribe as part of their ways aids in the cohesion of the group, helps that particular group to stand out and maintain its identity in the face of others and therefore creates a feeling of "belonging".
The meaning of the word taboo 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, religious beliefs, or cultural norms.
The English term taboo comes from tapu in Oceanic languages, particularly Polynesian languages, with such meanings as "prohibited" or "forbidden". That root tapu is reflected, among others, by Tongan or Māori tapu, and by Hawaiian kapu. Its English use dates to 1777 when the British explorer James Cook visited Tonga, and referred to the Tongans' use of the term taboo for "any thing that is forbidden to be eaten, or made use of". Having invited some of the Tongan aristocracy to dinner aboard his ship, Cook wrote:
Not one of them would sit down, or eat a bit of any thing. . . . On expressing my surprise at this, they were all taboo, as they said; which word has a very comprehensive meaning; but, in general, signifies that a thing is forbidden.