What is fire?

What you see and call the flame is actually glowing particles like ash, dust, and such whipped up by the heat of the rapid oxidation we call fire. We don't always see the fire.

For example, a clean fire off a gas stove top cannot be seen. It's invisible. OK maybe a little blue, but that's not complete combustion. The occasional flicker of orange perhaps is from some dust etc. that got caught in the heat.

So the heat of combustion, fire, is energy. It has the capability to do work or cause a change; to boil water for example. And during a fire that heat is carried off by convection and some radiation.

It is not plasma, that's at the atomic level. Fire is the result of a chemical reaction at the molecular level.

Fire is matter. It is usually a mixture of incandescent (hot, glowing) gas and particles produced in a rapid chemical reaction.

If the temperature is high enough some of the gas will be plasma (ionised gas).

It releases energy as heat and light. The energy comes from the chemical bonds of the reacting materials and is what raises the temperature.

It's a song by Arthur Brown. 1968, Bruce Springsteen 1977, the Ohio Players, 1974 and Gavin DeGraw 20?? I'm sure there other people who wrote songs of the same name but those are the most famous.

Fire is a plasma created by a chemical reaction.

Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction products.Slower oxidative processes like rusting or digestion are not included by this definition.

Fire is a self sustaining, rapid Oxidation reaction in a substance. Oxygen (usually from the surrounding air) will begin to REACT with a substance once that substance is heated to a sufficient degree to begin the reaction (the temperature may vary with the substance. (About 75 degrees for gasoline, 451F for paper, etc.)

Once the reaction begins it generates even more heat which maintains the reaction until the substance (called "fuel") is "consumed". The FUEL is not actually destroyed, but rather combines with oxygen to form other substances. The solid material formed is called ASH and Smoke, the latter being fine solids carried up into the air on heat currents. The other materials produced are gasses such as Carbon Dioxide (Co2) and Water (H2O) in vapor form--and depending on the fuel, other gasses may be released or produced in the action.
The FLAMES are only the hot gasses being released from the reaction---but heated so hot that they GLOW (not unlike a piece of metal heated in a fire) The heat causes them to rise, and the glow disappears as they rise high enough above the reaction to cool down a bit. ----So the flames are NOT the reaction, but rather released gasses from the reaction that have been heated yellow and red HOT.

Oxygen is needed to make a fire (rapid oxidation reaction), and most of the fires we see use the Oxygen in the surrounding air---but some substances, like gunpowder, use the oxygen in the chemicals that make it up. Divers can burn cutting torches UNDER WATER because the flames get the oxygen from a tank, and rockets also bring tanks of oxygen to make a fire in space.

Fire is a chemical reaction taking place at a molecular level generating heat and light energy.

Fire is a highly exothermic chemical reaction involving oxygen and a combustible material. The combustible material is oxidised. A hot flame is a plasma. Many things can burn including wood, metals such as sodium, magnesium and aluminium alloy, plastics and petroleum

Plasma is the fourth state of matter, the other three are solid, liquid and gas

Most people accept that fire is different from a glowing or smoldering coal.
Or from heat produced by a range of chemical reactions.

Fire is a gaseous reaction.
When sufficient heat is applied to a solid or a liquid it becomes dissociated and becomes a molecular gas.
When that combines with oxygen it releases heat energy which in turn dissociates more fuel.
Creating more gas and sustaining the reaction.
This self sustaining reaction is known as fire.

Now if you smother the flame by depriving it of oxygen temporarily, you can be left with the fuel still glowing, still producing heat and ultimately burning away fully. Yet few would call this "fire" even though it is fundamentally the same chemical reaction.
The main difference is that the fuel oxidizes on the surface where it interfaces with the air instead of being produced within the gas phase at some distance from the fuel.
This in turn sets a definite limit to the amount of heat which can be produced per second from a given surface area of fuel.

It is none of the above. It is a process.. Fire will burn your a**.
Not a plasma
Not energy
Not matter.

I like MD. MEHEDI HASAN 's answer.

Richard Feynman, who won the Nobel prize in physics was asked by a group pf Jewish scholars, "Is electricity fire?" He gave them a long answer and then found out they just wanted to ride the elevator.

http://www.amazon.com/Surely-Feynman-Adventures-Curious-Character/dp/0393316041