Rambutans are tropical fruits. Specifically, they are drupes, meaning they have a stone/pit.
They are quite obviously a fruit. They are tropical and sweet and eaten raw after being peeled. They basically taste like a vaguely tropical grape, except like a grape you have to peel first and then peel the fruit off the seed with your teeth. So like a grape you really have to work for. They are also very colorful and memorably designed, which makes sense for a fruit, since color helps attract polinators.