Ni-Vanuatu is a demonym

Demonym

A demonym , also referred to as a gentilic, is a name for a resident of a locality. A demonym is usually – though not always – derived from the name of the locality; thus, the demonym for the people of England is English, and the demonym for the people of Italy is Italian, yet, in english, the one...

 used to refer to all Melanesia

Melanesia

Melanesia is a subregion of Oceania extending from the western end of the Pacific Ocean to the Arafura Sea, and eastward to Fiji. The region comprises most of the islands immediately north and northeast of Australia...

n ethnicities originating in Vanuatu

Vanuatu

Vanuatu , officially the Republic of Vanuatu , is an island nation located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is some east of northern Australia, northeast of New Caledonia, west of Fiji, and southeast of the Solomon Islands, near New Guinea.Vanuatu was...

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It also refers, more generally, to nationals and citizens of Vanuatu, whatever their ethnicity.

NiVan is a commonly used abbreviation of ni-Vanuatu, which comes from the French née Vanuatu, meaning a citizen of (or otherwise someone that shares a sense of belonging with) the Republic of Vanuatu

Vanuatu

Vanuatu , officially the Republic of Vanuatu , is an island nation located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is some east of northern Australia, northeast of New Caledonia, west of Fiji, and southeast of the Solomon Islands, near New Guinea.Vanuatu was...

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