This giant citrus (citrus grandus) fruit is native to Malaysia (where it still grows abundantly). It is also cultivated in California and Israel. Most of the varieties found today have been bred and grown. A large pomelo is the largest of all citrus. They can grow to be as large as a foot in diameter and up to 25 pounds. The rind is very thick but soft and easy to peel away. The resulting fruit is light yellow to coral-pink flesh and can vary from juicy to slightly dry and from seductively spicy-sweet to tangy and tart. The pomelo is also known as a shaddock.
http://www.gourmetsleuth.com/pomelo.htm