The pummelo ( or pummelo or pommelo - or even "Shaddock" in some English speaking Caribbean countries ( where it was named after the sea captain that brought the first pummelo seeds to the West Indies ) is a large citrus fruit that is closely related to a grapefruit - but not quite. Its flesh is either white or a pinkish red and is quite sweet. It is not nearly as bitter as grapefruit can be. You'll notice upon cutting one open that it has a really thick pith ( the spongy inner part below the rind ) and membranes that separate the flesh that are extremely thick and are really considered inedible. Remove the membrane and discard before eating.
The pummelo is native to Asia and is often highlighted in Chinese and Vietnamese cooking.
Chose pummelos that are large and heavy, with little give to the flesh. It is ok to buy them with a greenish rind - they will ripen in the house quickly to a light green or pale yellow. They should have a citrus fragrance.
You eat a pummelo just like a grapefruit: cut it in half and scoop out the sections, or peel it and eat the sections. Either way, you'll probably want to not eat the membrane between the fruit.
If you like citrus fruits but aren't a huge grapefruit fan - the pummelo is for you. It isn't as bitter tart as a "normal" grapefruit but has a taste vaguely reminiscent of one. You'll be surprised at how thick the pith is on a pummelo, but will be rewarded for your peeling / scooping efforts with a beautiful pink or white fruit inside.