What Borders Tahiti? Nothing—It's an Island in French Polynesia

Tahiti has no land borders with any country. It is the largest island in the Windward group of the Society Islands, part of French Polynesia—an overseas collectivity of France in the South Pacific.

Geographic Context

• Coordinates: 17°40′S 149°25′W.
• Nearest neighbors (by sea): Moorea (17 km west), Tetiaroa (58 km north), Bora Bora (260 km northwest).
• Political status: French territory; residents are French citizens; EU associate member (OCT).
• EEZ: France claims a vast Exclusive Economic Zone around French Polynesia (~5 million km²).

So "what borders Tahiti?" → the Pacific Ocean (and administratively, the French Republic).