What fruit is this?

it's Jamboo

i love this fruit but call it differently in taiwan hehe

we call it in bisaya Philippines as tambis

In Malay, it is called Jambu Air (pronounced as "ayer").

we call it tambis in PH😂

we call it wax apple in the Caribbean. for us Jamun is a purple fruit we also call jar plum because it's shaped like a jar