What is the X in X-mas?
birthmark birth·mark (bûrth'märk')
A mole or blemish present on the skin from birth; a nevus.
congenital skin lesion, or birthmark, caused by abnormal pigmentation or by proliferation of blood vessels and other dermal or epidermal structures. Nevi may be raised or may spread along the surface of the skin. In other types, such as the blue nevus, proliferative tissue is buried deep within the dermis, the lower layer of the skin