A fetus is the developing stage of a human or animal after the embryonic stage and before birth. In humans, this stage begins around the 9th week of pregnancy and lasts until delivery. During this time, the fetus undergoes significant growth and development, forming essential organs and systems. Fetuses are nourished through the placenta, which connects them to the mother's bloodstream. This connection allows for the exchange of nutrients and waste products. The health and development of a fetus can be influenced by various factors, including maternal health, nutrition, and environmental conditions.