A taboo is a strong social prohibition (or ban) relating to any area of human activity or social custom declared as sacred and forbidden; breaking of the taboo is usually considered objectionable or abhorrent by society. The term was borrowed from the Tongan language and appears in many Polynesian cultures. In those cultures, a tabu (or tapu or kapu) often has specific religious associations. Its first use in English was recorded by James Cook in 1777.

When an activity or custom is classified as taboo it is forbidden and interdictions are implemented concerning the topic, such as the ground set apart as a sanctuary for criminals. Some taboo activities or customs are prohibited under law and transgressions may lead to severe penalties. Other taboos result in embarrassment, shame, and rudeness.

Taboos can include dietary restrictions (halal and kosher diets, religious vegetarianism, and the prohibition of cannibalism), restrictions on sexual activities and relationships (miscegenation, homosexuality, incest, zoophilia, pedophilia, necrophilia), restrictions of bodily functions (burping, flatulence), restrictions on the use of psychoactive drugs, restrictions on presence of genitalia (circumcision, sex reassignment), exposure of body parts (ankles in the Victorian British Empire, women's faces in Saudi Arabia and Afghanistan, nudity in the US), and restrictions on the use of offensive language.

No taboo is known to be universal, but some (such as the incest taboo) occur in the majority of societies. Taboos may serve many functions, and often remain in effect after the original reason behind them has expired. Some have argued that taboos therefore reveal the history of societies when other records are lacking.

Taboos often extend to cover discussion of taboo topics. This can result in taboo deformation (euphemism) or replacement of taboo words. Marvin Harris, a leading figure in cultural materialism, endeavoured to explain taboos as a consequence of the ecologic and economic conditions of their societies.

Also, Sigmund Freud provided an analysis of taboo behaviours, highlighting strong unconscious motivations driving such prohibitions. In this system, described in his collections of essays Totem and Taboo, Freud postulates a link between forbidden behaviours and the sanctification of objects to certain kinship groups.

Taboo and art

Many contemporary artists deal with taboo images and ideas including

• Matthew Barney
• Maurizio Cattalan
• Damien Hirst
• Joel-Peter Witkin
• Bill Viola

Film makers

• Pedro Almodóvar
• Luis Bunuel
• Derek Jarman