The Seder is the ritual banquet of Passover, and it tells the tale -- in both food and traditions -- of the Jewish exodus from Egypt.
At the center of the Seder celebration is the Seder table, and at the center of the Seder table is the Seder plate. The plate holds five or six foods (depending on the traditions of the family celebrating Passover), and each is steeped in symbolism:
Maror: Bitter herbs, signifying the bitterness of the slavery endured by the Jews in Egypt. This is usually horseradish root, although romaine lettuce and endive can be used. The more bitter and tear-inducing the maror, the more authentic it is.
Zeroa: A roasted shankbone, representing the sacrificial lamb offered at Passover feasts in the past. Chicken necks or, in vegetarian households, beets are sometimes used instead.
Charoset: A mixture of apples, nuts, spices, and wine, representing the mortar that Jewish slaves used while building the great structures of Egypt. The maror is usually dipped into the charoset to remove some of the maror's bitterness.
Chazeret: Depending on the traditions observed by the family performing the Seder, this can either be a bitter vegetable (usually a lettuce or radish) used in addition to the maror, or omitted entirely. The confusion stems from an interpretation of the commandment to "eat it (the sacrificial lamb) with unleavened bread and bitter herbs." Since "herbs" is plural, the charzeret is used in order to have more than one bitter item at the Seder.
Karpas: A vegetable, most often parsley or celery, that represents the coming of spring. The karpas is dipped in salt water, which is symbolic of the tears shed by the slaves in Egypt.
Beitzah: A roasted or baked egg, which is another symbol of spring -- and, according to some, a symbol of mourning. Eggs were a traditional offering, along with the sacrificial lamb, in biblical times. Many households will use brown eggs only.