A flame's the visible (light-emitting) part of a fire. It's caused by a highly exothermic reaction (for example, combustion, a self-sustaining oxidation reaction) taking place in a thin zone. If a fire's hot enough to ionize the gaseous components, it can become a plasma. The color and temperature of a flame are dependent on the type of fuel involved in the combustion, as, for example, when a lighter's held to a candle. The applied heat causes the fuel molecules in the wick to vaporize. In this… (More on Flame)