Final answer:
The fine, silky hair shed shortly after birth and replaced with vellus hair is called lanugo, which often disappears within the first few weeks of life.
Step-by-step explanation:
The baby's fine, silky hair that is shed shortly after birth and replaced with vellus hair is known as lanugo. During fetal development, particularly between the 17th and 20th weeks of gestation, lanugo grows on the fetus's skin as a form of protection and is usually shed before or shortly after birth. In some cases, especially in premature infants, this fine hair might still be present at birth but will typically disappear within the first few weeks of life.