What is stem cell?

Answer 1

A stem cell is a cell that can become any other kind of cell. In a tiny embryo, all of the cells are stem cells. By the time the fetus has developed, the fetus has muscle cells, nerve cells, skin cells, and all kinds of cells, all of which developed from stem cells.

Adults also have stem cells that are able to make new cells for our bodies.

Answer 2

The easiest way to consider this is to think of the stem of a mushroom. By the morning, that will be a full blown mushroom but you didn't even see it grow. But now it's in your yard.
So, placenta, or the sac a child is encapsulated in during a woman's gestation, is full with these stem cells. They could be anything that's needed...the new body will draw from these cells for whatever it needs. These cells, since they are stems, have been found through research to be able to form themselves into whatever cell is needed.
Perhaps the cells can be harvested once the woman gives birth. The baby is out and alive and the remainder stem cells are washed down the drain. Hmm. Shouldn't we save such things and look into the concept of using cells that can turn into anything as perhaps the cure to cancer? Our president says "no."