The etrog for this holiday
Etrog (Hebrew: אתרוג) is one of several varieties of citron, a citrus fruit of the orange and lemon family (Citrus medica var. Etrog). It is one of the Four Species used in a special waving ceremony during the Jewish holiday of Sukkot. The other species are the lulav (date palm frond), hadass (myrtle bough), and aravah (willow branch). (See Four Species for the complete description and symbolism of the waving ceremony.)
Leviticus 23:40 refers to the etrog as pri eitz hadar (פרי עץ הדר), which literally means, "a fruit of the beautiful tree." It can also be literally translated as "a fruit of a beautiful tree." Modern Hebrew translates hadar as "citrus," in connection with the rabbinical definition of the etrog as the fruit referred to by the Torah. The Arabic name for the fruit, itranj اترنج is cognate with the Hebrew. The itranj is mentioned favorably in the hadith.
The etrog is a slow-growing fruit. The citron tree is typically grown from cuttings that are two to four years old; the tree begins to bear fruit when it is around three years old. The fruit is oblong in shape, and sometimes as much as six inches in length. Its skin is thick, somewhat hard, fragrant, and covered with protuberances; the pulp is white and subacid. It is typically bought before the holiday of Sukkot while it is still green, and ripens to a deep yellow during the course of the holiday.