What is the ball of cells called in the reproductive system?

In the reproductive system, the ball of cells is called a blastocyst. It forms after the fertilization of an egg and undergoes several divisions, eventually developing into a hollow structure that implants into the uterine wall during early pregnancy. The blastocyst consists of an inner cell mass that will become the embryo and an outer layer called the trophoblast that will contribute to forming the placenta.