What is Fire?

Fire is awesome.

That's a simple enough answer, isn't it?

This video - with its oddly-voiced, slightly-speech-impedimented (or maybe just a British accent), and weird narrator - explains a bit of the history of elements and then goes through the parts that really make up the fire: fuel, gas, light, heat.

In the end, the answer to the video's titular question is this: Fire is actually the visible side effect of what happens when matter undergoes a change of state by means of a chemical reaction. (at 1:15 in the video)