Lulov and Etrog Sets
The four species are four plants mentioned in the Torah as being relevant to Sukkot. Karaite Jews build their Sukkot out of branches from the four specified plants, while Rabbinic Jews take three types of branches and one type of fruit which are held together and waved in a special ceremony during the Jewish holiday of Sukkot. The waving of the four plants is a mitzvah prescribed by the Torah, and contains symbolic allusions to a Jew's service of God.
In Talmudic tradition, the four plants are identified as:
Etrog – the fruit of a citron tree
Lulov – a ripe, green, closed frond from a date palm tree
Hadass – boughs with leaves from the myrtle tree
Aravah – branches with leaves from the willow tree