The origin and definition of brite versus white and classical brown adipocytes

White adipose tissue stores energy while brown adipose tissue contributes to body temperature maintenance through non-shivering thermogenesis. In addition, brite (brown-in-white) adipocytes resembling classical brown adipocytes within predominantly white adipose tissue can be found in response to cold adaptation or other stimuli. Even though our understanding of brite adipocyte formation has increased substantially in the last few years, it is still unclear how brite and classical brown adipocytes are formed in vivo. In this review, we outline and discuss the current understanding of brite adipocyte nomenclature, developmental origin and possible mechanisms of their recruitment. We reason that future work in the field will bridge in vivo tracing studies and primary cell characterization with molecular mechanistic data from in vitro approaches to devise new means to increase energy expenditure.