The beitzah (ביצה) is an egg. (You’ve heard of them before.) To prepare this one, simply hard boil an egg, then give it a little roast on the stove-top on inside the oven while the shell still encloses it. The egg serves as another reminder of the special holiday sacrifice offering, which was called the hagigah.
The roundness of the egg also symbolizes the cycle of life, the continuous flow between life to death to rebirth, and the springtime renewal of Passover.