Provide definitions/explanations for the following terms:
$(1)$ Embryo
$(2)$ Proliferation phase

(N/A) $(1)$ The embryo is the early stage of development of a multicellular diploid eukaryotic organism. In humans,it refers to the product of conception from the time of implantation in the uterine wall until the end of the $8^{th}$ week of gestation.
$(2)$ The proliferation phase,also known as the follicular phase or proliferative phase,is the period of the menstrual cycle occurring between days $6$ and $14$. During this phase,the primary follicles in the ovary grow to become a fully mature Graafian follicle,and the endometrium of the uterus regenerates through proliferation.