Etrog

Etrog (Hebrew: אֶתְרוֹג‎) refers to the yellow citron or Citrus medica used by Jews on the week-long holiday of Sukkot.

While in modern Hebrew this is the name for any variety citron, its English usage is commonly applied only to those varieties and specimens typically used for the Jewish ritual as one of the Four species. In any case, it doesn't apply only to one specific variety.
The romanization as Etrog is according to the Sephardic pronunciation, widely used in Israel through Modern Hebrew. The Ashkenazi pronunciation as in Yiddish, is esrog or esrig. Rarely it could also be transliterated as Ethrog even in scholarly work, which is according to the Yemenite Hebrew.

The fruit is typically picked while still green, taking advantage of ethylene gas to ripen the fruit in a controlled manner. The same gas is also naturally released from apples, so some growers simply put the fruits in the same box as apples. The etrog used in the mitzvah of the four species must be largely unblemished, with the fewest black specks or other flaws. Extra special care is needed to cut around the leaves and thorns that may scratch the fruit. It is also important to protect the fruit-bearing trees from any dust and carbon, which may get caught in the stomata of the fruit during growth, and may later appear as a black dot.

Source: http://en.wikipedia.org/wiki/Etrog
See Also: bunga, toko bunga, bunga papan