Karpas - The Spring Greens
Karpas (כרפס) are the green leafy vegetables used on the seder plate for Passover. Usually, a piece of green parsley is used, though any leafy green can suffice. Some folks even use potatoes.
Karpas serves as a symbol of the wonderful bounty of vegetables and fruits in the springtime harvest. It also represents the period of Jewish flourishing before the period of Egyptian slavery began. This flourishing is meant both metaphorically and literally--in the Torah, we are told that the Israelites numbered 70 individuals when Jacob and his family descended into Egypt. A few generations later, due to a prodigious birthrate, they consisted of hundreds of thousands.