A Mongolian spot, also known as slate grey nevus or congenital dermal melanocytosis, is a benign, flat, congenital birthmark with wavy borders and an irregular shape. In 1883, it was described and named after Mongolians by Erwin Bälz, a German anthropologist based in Japan, who erroneously believed it to be most prevalent among his Mongolian patients. It normally disappears three to five years after birth and almost always by puberty. The most common color is blue, although they can be blue-gray, blue-black or deep brown. Cause
Mongolian spot is a congenital developmental condition—that is, one existing from birth—exclusively involving the skin. The blue colour is caused by melanocytes, melanin-containing cells, that are usually located in the surface of the skin (the epidermis), but are in the deeper region (the dermis) in the location of the spot. Usually, as multiple spots or one large patch, it covers one or more of the lumbosacral area (lower back), the buttocks, sides, and shoulders. It results from the entrapment of melanocytes in the lower half to two-thirds of the dermis during their migration from the neural crest to the epidermis during embryonic development.Male and female infants are equally predisposed to slate grey nevus. People who are not aware of the background of the slate grey nevus may mistake them for bruises, possibly resulting in mistaken concerns about abuse.
Activity may refer to:

Action (philosophy), in general
Human activity: human behavior, in sociology behavior may refer to all basic human actions, economics may study human economic activities and along with cybernetics and psychology may study their modulation
Recreation, or activities of leisure
The Aristotelian concept of energeia, Latinized as actus
Activity (UML), a major task in Unified Modeling Language
Activity, the rate of catalytic activity, such as enzyme activity (enzyme assay), in physical chemistry and enzymology
Thermodynamic activity, the effective concentration of a solute for the purposes of  mass action
Activity (project management)
Activity, the number of radioactive decays per second
Activity (software engineering)
Activity (soil mechanics)
HMS Activity (D94), an aircraft carrier of the Royal Navy
"Activity", a song by Way Out West from Intensify
Cultural activities, activities referred to culture. See also
Activity theory, a learning theory in education
Social activity (disambiguation), several concepts in the social sciences
Activiti (software), an open source Business Process Management platform
Active (disambiguation)