1. The embryo is the developing baby in the first eight weeks of pregnancy.

2. The foetus is the developing baby from eight weeks of pregnancy to birth.

3. A zygote is a fertilised egg cell.

4. A blastocyst is a hollow ball of cells which floats around in the uterus for three to four days before it implants.

5. The trophoblast is the single layer of cells around the outside of the blastocyst.

6. Implantation is when the blastocyst becomes embedded in the wall of the uterus, usually occurring seven to nine days after conception.
(The cells of the trophoblast actually dig into the wall of the uterus and start to digest the cells in the uterus, providing a source of nourishment for the embryo.)

7. The amniotic fluid is the watery liquid in which the baby floats, within the uterus, until birth.

8. The chorion is the outer embryonic membrane, which originated from the trophoblast, and which sends villi into the wall of the uterus.

9. Gastrulation is the process by which the three primary tissues are formed.