Sirenomelia, also known as Mermaid syndrome, is a rare congenital disorder in which a baby is born with partially or completely fused legs. There are several synonyms used to refer to this condition in medical literature, including symmelia, symposia, sympodia, pseudo-mermaid syndrome, and caudal regression syndrome. Symmelia is derived from the Greek word "syn" meaning together and "melos" meaning limb. Symposia and sympodia are also derived from the Greek language, with symposia referring to a congenital absence of the lower limbs, and sympodia denoting the fusion of the lower limbs. Pseudo-mermaid syndrome is a layman's term used to describe the condition due to the fusion of the lower limbs resembling a mermaid's tail. Lastly, caudal regression syndrome encompasses multiple congenital abnormalities, including sirenomelia.