Final answer:
The endometrium is the inner lining of the uterus, comprising the stratum basalis and the stratum functionalis, which thickens for potential embryo implantation and sheds during menstruation if fertilization doesn't happen.
Step-by-step explanation:
The endometrium is the innermost layer of the uterus, essential for reproductive functions. It consists of two sub-layers: the stratum basalis, which remains after menstruation, and the stratum functionalis, which grows and thickens in response to hormones, providing a site for implantation and shedding if no fertilization occurs. The endometrium plays a crucial role in the menstrual cycle and potential pregnancy.