Saint Martin, Saint-Martin, and Sint Maarten
Saint Martin is what the Caribbean island is called as a whole.
Saint-Martin refers to the French side of the island in the north half. It's known for its nude beaches and french cuisine.
Sint Maarten refers to the Dutch side of the island in the southern half. This part of the island is generally considered more "Caribbean," more diverse, and is quite a bit more industrious. The main airport, cruise port, and many more buildings are on this side of the island.