In chemistry, something that's exothermic has to do with the release of heat. Burning a candle is an exothermic process, since heat is given off.
The scientific adjective exothermic is good for describing reactions that involve releasing energy, usually in the form of heat. Exothermic processes vary from something as simple as striking a match on a rough surface to a more extreme and violent example — an explosion. Part of what defines an exothermic reaction is that more energy is released than was required to start it. The word's Greek roots are exo, "outside," and therme, "heat."