Exothermic

In thermodynamics, the term exothermic ("outside heating") describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light (e.g. a spark, flame, or explosion), electricity (e.g. a battery), or sound (e.g. burning hydrogen). Its etymology stems from the prefix exo (derived from the Greek word ἔξω, exō, "outside") and the Greek word thermasi (meaning "to heat"). The term exothermic was first coined by Marcellin Berthelot. The opposite of an exothermic process is an endothermic process, one that absorbs energy in the form of heat.