Tapu (or tabu) is a concept existing in many Polynesian societies, including traditional Hawaiian, Tongan, and Maori cultures. It reflects something that is holy or sacred.
In the Hawaiian belief system, everything starts out with tapu, but misdeeds make it lose its tapu. See: kapu.
In Maori and Tongan tradition, something that is tapu (Maori) or tabu (Tongan) is considered inviolable or sacrosanct due to its sacredness. Things or places which are tapu must be left alone, and may not be approached or interfered with. In some cases, they should not even be spoken of.
The English word “taboo” derives from this usage, and was adopted by Captain James Cook during his visit to Tonga in 1777.