Lanugo pertains to the fine hair that covers a newborn baby, serving as an insulating layer. There are several synonyms for the term, such as vellus hair, primary hair, and prenatal hair. Vellus hair refers to the soft and fine hair present throughout the body of an individual, while primary hair comprises the first hair that grows at the fetal stage. Prenatal hair, on the other hand, is the term used to describe the hair that covers the skin of a fetus. These synonyms serve as alternative ways of referring to the same concept, and using them in writing or conversation can provide variety and clarity in communication.