What is fire?

What kind of matter is the flame or fire?
A solid : definitely not-no proper structure, shape ,density.
A liquid: obviously no chance-no flow towards lower regions,not affected by gravity.
Gaseous: A gas must flow from denser to rarer region.But the flame doesn't.

Think beyond the sky........

How could a flame burn from a candle in space inside a spaceship filled with air(O2)...
Hint:Flame burns upright due to hot air ascending up because of earth's Gravity...causing cold air descending down due its more weight...In space there is no gravity.