fat cell brown fat cell A cell from the thermogenic form of adipose tissue found in many species, particularly in newborns and hibernating mammals, but also in lesser amounts in adults of other mammals including humans. Brown fat is capable of rapid liberation of energy and seems to be important in the maintenance of body temperature immediately after birth and upon waking from hibernation. CALOHA:TS-0099 FMA:83435 brown adipocyte brown adipose cell