Well, it seems like after the 8th week it's called a fetus, but before it's just an embryo.
Week four
The embryo lasts until about week 10 or 11 and then it is known as a fetus.
In humans, the prefetal product of conception from implantation through the eighth week of development.
Embryo, between the 3rd and 8th week. Fetus, after the 8th week
4th week
The women has been pregnant for a week, although most doctors count from the date since the woman's last period.
about the size of a small lamb
During week one, the embryo is still at the stage of implantation and does not have a measurable length. By the end of week ten, the embryo has developed into a fetus and is typically around 1.2 to 1.6 inches (3 to 4 centimeters) long.
At 5 weeks it's a embryo not a fetus. it just grows and can not feel, hear or is aware of anything yet.
The sperm fertilizes the egg and it begins to grow as an embryo. During the eight week of development it becomes recognizable as being human and is called a fetus.
The name given to the human organism two to eight weeks after fertilization is an embryo.