The term syndactyly refers to:

Syndactyly is specifically defined as the condition where two or more fingers or toes are fused together. This fusion can involve soft tissue, bone, or both, and it occurs during fetal development when the separation of digits does not occur as it normally would. Understanding this term is important in the context of congenital conditions and limb development.

The other terms in the choices relate to different concepts. A vascular malformation refers to an abnormal formation of blood vessels and is unrelated to the fusion of digits. The mention of a second row of eyelashes does not correlate with syndactyly but represents a different type of congenital malformation known as distichiasis. Bony hypertrophy pertains to the enlargement of bones, rather than their fusion. Therefore, recognizing syndactyly as the fusion of toes is accurate within the context of congenital anomalies affecting limb structure.