Thermogenic means tending to produce heat, and the term is commonly applied to drugs which increase heat through metabolic stimulation, or to microorganisms which create heat within organic waste.
In bodybuilding, athletes wishing to lose fat purportedly use thermogenics to increase their basal metabolic rate, thereby increasing their energy expenditure. Caffeine and ephedrine are commonly used for this purpose. 2,4-Dinitrophenol (DNP) is a very dangerous thermogenic drug used for fat loss; it will give a dose-dependant increase in body temperature, to the point where it can induce death by hyperthermia. It works as a mitochondrial oxidative phosphorylation uncoupler, disrupting the mitochondrial electron transport chain. This stops the mitochondria from producing adenosine triphosphate, releasing energy as heat.