Brown adipose tissue is a specialised fat that burns energy to produce heat rather than storing it. Unlike white fat, its cells are packed with mitochondria containing uncoupling protein 1, which short-circuits normal energy production to release warmth, a process called non-shivering thermogenesis. Abundant in newborns and hibernating animals, it was long thought absent in adults until imaging revealed active deposits around the neck and spine. Cold exposure activates it, and researchers are investigating whether stimulating brown fat could help manage obesity. Its discovery reshaped the view of adipose tissue from passive storage to metabolically dynamic organ.