What Kind of Fruit Are These?

About the size of apricots, they contain 3-5 large brown seeds shaped like wedges taken out of a sphere.

The flesh is less than 1/4" thick. It has a mild, slightly tart taste. Kind of a generic fruit flavor. It's not gonna be the next kiwi, believe me.
The label in the store read nisperos. Do any of you know what it's called in English? Or its botanical name?