A exothermic reaction is the type of reaction that releases energy, usually in the form of heat and light. Such reactions occur when the total energy of the products is lower than that of the reactants, leading to a net release of energy. Common examples include combustion reactions, like burning fossil fuels, and cellular respiration in living organisms. Understanding exothermic reactions is crucial in fields like thermodynamics, chemistry, and engineering, as they can have significant implications for energy production and consumption.